### Summary
This merge request adds a horizontal bar at top of room list, which shows spaces. By clicking on a space, user can filter out rooms belonging only to that specific space.
### Pending/ Help needed
#### Segfault when loading active connection on startup
Refer `void SortFilterRoomListModel::cacheSpaceHierarchy()` ([link](8c372800d7 (b969e462c30df43ef3714ea441948d8d8027f6a0_117_126))) in `src/sortfilterroomlistmodel.cpp`.
On [line 129](8c372800d7 (b969e462c30df43ef3714ea441948d8d8027f6a0_117_129)), I have called `connection->allRooms()`, which segfaults if the active connection hasn't been loaded yet. Is there a way to ensure that `Controller::instance().activeConnection()` on line 128 waits till connection is loaded?
#### Avatars
Avatars on space horizontal bar aren't aligned to vertical middle. I'll need help with that.
Using the code below doesn't help with padding
```qml
delegate: QQC2.Control {
topPadding: 10
contentItem: Kirigami.Avatar { ..... }
}
```
This complains about uninitialized properties in `Kirigami.Avatar`. (`id`, `currentRoom`, `avatar`, `index` are properties utilized during run time)
After we get around these two issue, this MR will be ready from my side.
Fix laggish RoomListView when dragging.
Remove per-room timer and add timer in RoomForm.
Remove singleton module and use file as singleton.
Minor UI tweak in RoomListView.
Pass room to RoomListView via "currentRoom" delegate property and remove
RoomListForm-wide currentRoom.
Put menu files in a separate folder.
Show initial image in ImageStatus when avatar is not loaded.
Add about page.
Merge all setting pages into Setting.qml.
Add option to rearrange rooms by activity.
Add option to use RichText parser.
Add document url.
