Chat-ng filters and search #3029

as part of the efforts to make chat great, we want to revisit the way the filter and search chat rooms.

The main feedback is around: the sticky filters are nice, though putting that into the title only is a bit hidden. Having them applied for search is a crux though, if you are looking for things not already in the filtered list, you have to disable the filter, then find the thing, then re-enable the filter. Instead we want:

1. Split search and filtering: filters apply to the main view, search becomes its own sub-page without any filtering (which later could be extended over not-yet joined rooms)
2. rework the appbar: keep the same title, remove the filter-icon, only have the search-icon
3. filters visibility: without the filter-icon, they are by default only available via pull-down, but always show them all when one is selected. Move the selected to the left next to "all", and use it as a toggle to disable it.
4. A new filter for "groups" that creates space-ordered sections of chats for the chats assigned. Might not be 100% clean as chats can appear multiple times, but is a requested features for better "overview". (there is a good chance we spin this off into its own ticket later)

Balsamiqs here.