Support pushrules and notifications on keywords

[KitsuneRal]

Once a highlight is indicated by the server, there's no other way but to visually scout through the backlog for keywords. Things to implement:

• [ ] Enable loading the list of keywords/pushrules from the server
• [ ] Enable sending the locally configured list of keywords/pushrules to the server
• [ ] Implement the event highlighting logic (a crude version of which is now in QuaternionRoom::isEventHighlighted)