FEATURE: Native theme support

This feature introduces the concept of themes. Themes are an evolution
of site customizations.

Themes introduce two very big conceptual changes:

- A theme may include other "child themes", children can include grand
children and so on.

- A theme may specify a color scheme

The change does away with the idea of "enabled" color schemes.

It also adds a bunch of big niceties like

- You can source a theme from a git repo

- History for themes is much improved

- You can only have a single enabled theme. Themes can be selected by
    users, if you opt for it.

On a technical level this change comes with a whole bunch of goodies

- All CSS is now compiled using a custom pipeline that uses libsass
    see /lib/stylesheet

- There is a single pipeline for css compilation (in the past we used
    one for customizations and another one for the rest of the app

- The stylesheet pipeline is now divorced of sprockets, there is no
   reliance on sprockets for CSS bundling

- CSS is generated with source maps everywhere (including themes) this
    makes debugging much easier

- Our "live reloader" is smarter and avoid a flash of unstyled content
   we run a file watcher in "puma" in dev so you no longer need to run
   rake autospec to watch for CSS changes

config/routes.rb

@@ -56,8 +56,6 @@ Discourse::Application.routes.draw do
   get "site/basic-info" => 'site#basic_info'
   get "site/statistics" => 'site#statistics'
 
-  get "site_customizations/:key" => "site_customizations#show"
-
   get "srv/status" => "forums#status"
 
   get "wizard" => "wizard#index"
@@ -162,6 +160,7 @@ Discourse::Application.routes.draw do
 
     scope "/logs" do
       resources :staff_action_logs,     only: [:index]
+      get 'staff_action_logs/:id/diff' => 'staff_action_logs#diff'
       resources :screened_emails,       only: [:index, :destroy]
       resources :screened_ip_addresses, only: [:index, :create, :update, :destroy] do
         collection do
@@ -174,9 +173,9 @@ Discourse::Application.routes.draw do
     get "/logs" => "staff_action_logs#index"
 
     get "customize" => "color_schemes#index", constraints: AdminConstraint.new
-    get "customize/css_html" => "site_customizations#index", constraints: AdminConstraint.new
-    get "customize/css_html/:id/:section" => "site_customizations#index", constraints: AdminConstraint.new
+    get "customize/themes" => "themes#index", constraints: AdminConstraint.new
     get "customize/colors" => "color_schemes#index", constraints: AdminConstraint.new
+    get "customize/colors/:id" => "color_schemes#index", constraints: AdminConstraint.new
     get "customize/permalinks" => "permalinks#index", constraints: AdminConstraint.new
     get "customize/embedding" => "embedding#show", constraints: AdminConstraint.new
     put "customize/embedding" => "embedding#update", constraints: AdminConstraint.new
@@ -186,12 +185,17 @@ Discourse::Application.routes.draw do
     post "flags/agree/:id" => "flags#agree"
     post "flags/disagree/:id" => "flags#disagree"
     post "flags/defer/:id" => "flags#defer"
-    resources :site_customizations, constraints: AdminConstraint.new
+
+    resources :themes, constraints: AdminConstraint.new
+    post "themes/import" => "themes#import"
 
     scope "/customize", constraints: AdminConstraint.new do
       resources :user_fields, constraints: AdminConstraint.new
       resources :emojis, constraints: AdminConstraint.new
 
+      get 'themes/:id/:target/:field_name/edit' => 'themes#index'
+      get 'themes/:id' => 'themes#index'
+
       # They have periods in their URLs often:
       get 'site_texts'          => 'site_texts#index'
       get 'site_texts/(:id)'    => 'site_texts#show',   constraints: { id: /[\w.\-]+/i }
@@ -385,7 +389,8 @@ Discourse::Application.routes.draw do
 
   get "highlight-js/:hostname/:version.js" => "highlight_js#show", format: false, constraints: { hostname: /[\w\.-]+/ }
 
-  get "stylesheets/:name.css" => "stylesheets#show", constraints: { name: /[a-z0-9_]+/ }
+  get "stylesheets/:name.css.map" => "stylesheets#show_source_map", constraints: { name: /[-a-z0-9_]+/ }
+  get "stylesheets/:name.css" => "stylesheets#show", constraints: { name: /[-a-z0-9_]+/ }
 
   post "uploads" => "uploads#create"
 
@@ -708,6 +713,8 @@ Discourse::Application.routes.draw do
   get "/safe-mode" => "safe_mode#index"
   post "/safe-mode" => "safe_mode#enter", as: "safe_mode_enter"
 
+  get "/themes/assets/:key" => "themes#assets"
+
   get "*url", to: 'permalinks#show', constraints: PermalinkConstraint.new
 
 end