FEATURE: Ability to add components to all themes (#8404)

* FEATURE: Ability to add components to all themes

This is the first and functional step from that topic https://dev.discourse.org/t/adding-a-theme-component-is-too-much-work/15398/16

The idea here is that when a new component is added, the user can easily assign it to all themes (parents).

To achieve that, I needed to change a site-setting component to accept `setDefaultValues` action and `setDefaultValuesLabel` translated label.
Also, I needed to add `allowAny` option to disable that for theme selector.

I also refactored backend to accept both parent and child ids with one method to avoid duplication (Renamed `add_child_theme!` to more general `add_relative_theme!`)

* FIX: Improvement after code review

* FIX: Improvement after code review2

* FIX: use mapBy and filterBy directly

app/models/theme.rb

@@ -376,10 +376,15 @@ class Theme < ActiveRecord::Base
     fields.values
   end
 
-  def add_child_theme!(theme)
-    new_relation = child_theme_relation.new(child_theme_id: theme.id)
+  def add_relative_theme!(kind, theme)
+    new_relation = if kind == :child
+      child_theme_relation.new(child_theme_id: theme.id)
+    else
+      parent_theme_relation.new(parent_theme_id: theme.id)
+    end
     if new_relation.save
       child_themes.reload
+      parent_themes.reload
       save!
       Theme.clear_cache!
     else