Add handling for new default push rules added in 1.7 also add a generic unknown handling for if any others are added in the future so they don't appear in keywords
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
