Refactor theme fields so they support custom theme defined vars

This paves the way to allowing themes to specify uploads and so on.

spec/controllers/admin/staff_action_logs_controller_spec.rb

@@ -19,12 +19,12 @@ describe Admin::StaffActionLogsController do
   context '.diff' do
     it 'can generate diffs for theme changes' do
       theme = Theme.new(user_id: -1, name: 'bob')
-      theme.set_field(:mobile, :scss, 'body {.up}')
-      theme.set_field(:common, :scss, 'omit-dupe')
+      theme.set_field(target: :mobile, name: :scss, value: 'body {.up}')
+      theme.set_field(target: :common, name: :scss, value: 'omit-dupe')
 
       original_json = ThemeSerializer.new(theme, root: false).to_json
 
-      theme.set_field(:mobile, :scss, 'body {.down}')
+      theme.set_field(target: :mobile, name: :scss, value: 'body {.down}')
 
       record = StaffActionLogger.new(Discourse.system_user)
         .log_theme_change(original_json, theme)

spec/controllers/admin/themes_controller_spec.rb

@@ -14,8 +14,8 @@ describe Admin::ThemesController do
     context ' .index' do
       it 'returns success' do
         theme = Theme.new(name: 'my name', user_id: -1)
-        theme.set_field(:common, :scss, '.body{color: black;}')
-        theme.set_field(:desktop, :after_header, '<b>test</b>')
+        theme.set_field(target: :common, name: :scss, value: '.body{color: black;}')
+        theme.set_field(target: :desktop, name: :after_header, value: '<b>test</b>')
 
         theme.remote_theme = RemoteTheme.new(
           remote_url: 'awesome.git',
@@ -71,7 +71,7 @@ describe Admin::ThemesController do
       it 'updates a theme' do
         #focus
         theme = Theme.new(name: 'my name', user_id: -1)
-        theme.set_field(:common, :scss, '.body{color: black;}')
+        theme.set_field(target: :common, name: :scss, value: '.body{color: black;}')
         theme.save
 
         child_theme = Theme.create(name: 'my name', user_id: -1)