Massive refactor

- Use contextual namespaces within Flarum\Core
- Clean up and docblock everything
- Refactor Activity/Notification blueprint stuff
- Refactor Formatter stuff
- Refactor Search stuff
- Upgrade to JSON-API 1.0
- Removed “addedPosts” and “removedPosts” relationships from discussion
API. This was used for adding/removing event posts after renaming a
discussion etc. Instead we should make an additional request to get all
new posts

Todo:
- Fix Extenders and extensions
- Get rid of repository interfaces
- Fix other bugs I’ve inevitably introduced

framework/core/src/Assets/AssetManager.php

@@ -1,6 +1,6 @@
 <?php namespace Flarum\Assets;
 
-use RuntimeException;
+use DomainException;
 
 class AssetManager
 {
@@ -29,7 +29,7 @@ class AssetManager
                 break;
 
             default:
-                throw new RuntimeException('Unsupported asset type: '.$ext);
+                throw new DomainException('Unsupported asset type: '.$ext);
         }
     }