Change the LastActivity sort order to Activity and update to a more flexible way of sorting based on an order from model roles.
Add options to actually switch between Alphabetical and Activity
Based on some old work by @tdfischer
implements #103
The aim is to be able to use separate delegate for things like codeblocks and quotes so that they can be styled differently.

Currently the ability to reply in threads was added but not the ability to actually view threads so this doesn't currently make much sense to just have enabled int he main build.
Note: I want to cherrypick this so it's just the flag. I'll add a feature flag page to dev tools for master soon.
Currently, this is only to pause playback of other media when something new starts playing.
In the future, it will also be used for other things, like call ringing, etc.
This is the first step in separation, so we can focus more on the
actions in this menu, and it's not tangled up in how the context menu is
shown and displayed.
This handles the following non-functioning cases from the space saving mr:
- Selecting home or friends
- Switching space that has the same room selected
For now everything should look identical. However this moves to using a model for the content of the message and is intended to lay the foundation for improved message content representation, e.g. splitting up a text message in multiple sections and using different delegates for things like code and quotes.
According to the HIG, scrolling should be kept to a minimum on settings
dialogs. The default window size for the dialog is too small on desktop,
and usually needs to be resized to prevent scrolling.
- When click on a space the space home page is shown, unless the current room is also a member of the new space
- When changing to friends or global the first is entered
- The global now only contains rooms that are not part of a space
- Global is now home
Get rid of the anchors and move to layouts for th bubble and avatars.
This allows the timestamp to be fixed in compact mode so it always sits on the far right. It's also just now more compact than before.

Make the user search automatically. This includes a timer to ensure that we aren't constantly pinging the server as the user types, the search is started 0.5s after the user stops typing. The `PublicRoomListModel` is upgraded to work in the same manner as it was architected slightly differently.