### 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.
This works around limitations of Qt's rich text detection and prevents
some messages from being shown wrong, like in #532.
In theory it is not ideal to send every message as HTML, however it's
not a significant problem and we already do it for edits and replies
(which also explains why edited messages are sometimes magically
rendered correctly while the original is not).
This adds support for displaying recieved spoilers, but not sending
them. Spoilers are displayed as a black rectangle, and can be clicked on
to be revealed. If the last message in a channel was a spoiler, it is
not shown on the left sidebar.
The spoiler blackening is done in CSS, but to check if a message
contains a spoiler for determining if it should cause a different cursor
to be displayed and if it should be shown in the sidebar, a simple check
of if the message contains "data-mx-spoiler" is used.
* Message with multiple mentions are not broken in IRC. Fix#267
* Editing a message won't remove mentions anymore
(cherry picked from commit bb3b3bc088)
