Push Rule Model Rework

This is a significant rework of the handling of push rules. Rather than using a lot of boilerplate code for the default models `KeywordNotificationModel` has been converted to `PushRuleModel` and now handles all push rules.

The new model has the following features:
- Handles all push rules
- Has special handling for the names of default keywords (i.e. it still gives the same text as previously for showing in the settings menus)
- Push rules for blocking individuals or room overrides are still there but hidden so will be available for developer tools (to follow)
- Room specific keywords are now supported.

The notification settings pages have also been refactored to take advantage of the new models. Each section is now just a repeater with a filter for the rules that it should contain. The push rule delegate has now been cleaned up and uses required properties.

Implements network/neochat#574

src/neochatconfig.kcfg

@@ -54,6 +54,10 @@
     <entry name="LastSaveDirectory" type="String">
       <label>Directory last used for saving a file</label>
     </entry>
+    <entry name="KeywordPushRuleDefault" type="int">
+      <label>The default setting for a new keyword push rule.</label>
+      <default>4</default>
+    </entry>
   </group>
   <group name="Timeline">
     <entry name="ShowAvatarInTimeline" type="bool">