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

spec/components/stylesheet/manager_spec.rb

@@ -0,0 +1,57 @@
+require 'rails_helper'
+require 'stylesheet/compiler'
+
+describe Stylesheet::Manager do
+  it 'can correctly compile theme css' do
+    theme = Theme.new(
+      name: 'parent',
+      user_id: -1
+    )
+
+    theme.set_field(:common, "scss", ".common{.scss{color: red;}}")
+    theme.set_field(:desktop, "scss", ".desktop{.scss{color: red;}}")
+    theme.set_field(:mobile, "scss", ".mobile{.scss{color: red;}}")
+    theme.set_field(:common, "embedded_scss", ".embedded{.scss{color: red;}}")
+
+    theme.save!
+
+
+    child_theme = Theme.new(
+      name: 'parent',
+      user_id: -1,
+    )
+
+    child_theme.set_field(:common, "scss", ".child_common{.scss{color: red;}}")
+    child_theme.set_field(:desktop, "scss", ".child_desktop{.scss{color: red;}}")
+    child_theme.set_field(:mobile, "scss", ".child_mobile{.scss{color: red;}}")
+    child_theme.set_field(:common, "embedded_scss", ".child_embedded{.scss{color: red;}}")
+    child_theme.save!
+
+    theme.add_child_theme!(child_theme)
+
+    old_link = Stylesheet::Manager.stylesheet_link_tag(:desktop_theme, 'all', theme.key)
+
+    manager = Stylesheet::Manager.new(:desktop_theme, theme.key)
+    manager.compile(force: true)
+
+    css = File.read(manager.stylesheet_fullpath)
+    _source_map = File.read(manager.source_map_fullpath)
+
+    expect(css).to match(/child_common/)
+    expect(css).to match(/child_desktop/)
+    expect(css).to match(/\.common/)
+    expect(css).to match(/\.desktop/)
+
+
+    child_theme.set_field(:desktop, :scss, ".nothing{color: green;}")
+    child_theme.save!
+
+    new_link = Stylesheet::Manager.stylesheet_link_tag(:desktop_theme, 'all', theme.key)
+
+    expect(new_link).not_to eq(old_link)
+
+    # our theme better have a name with the theme_id as part of it
+    expect(new_link).to include("/stylesheets/desktop_theme_#{theme.id}_")
+  end
+end
+