- Have LinkPreviewers stored in NeoChatConnection so that they don't have to be reloaded everytime the MessageContentModel is refreshed
- This means the link is never changed (it will be swiched for a new previewer with the new link)
- LinkPreviewers are stored by URL so they can be re-used by any event with the same URL
BUG: 484927 (because the offending code is ripped out)
This draws heavily on what @carlschwan did in network/neochat!1579 but I found it easier to start again and grab the bits as I needed them plus some other copying from what I did in the Space tree model.
From my current limited testing this seems to work nicely try and break it.
Shutup qt about below
```
SortFilterRoomListModel is neither a QObject, nor default- and copy-constructible, nor uncreatable. You should not use it as a QML type.
SortFilterRoomTreeModel is neither a QObject, nor default- and copy-constructible, nor uncreatable. You should not use it as a QML type.
SortFilterSpaceListModel is neither a QObject, nor default- and copy-constructible, nor uncreatable. You should not use it as a QML type.
```
Move the various room models into RoomManager. This means the same room models are always used and is a base from which further logic can be moved from QML to cpp.
Fixes#645
- Active space handling is moved from QML to RoomManager
- Active tab in SpaceDrawer (space / no space / DM) is unified in a single variable
- RoomList & RoomPage loading is simplified: We're always pushing a RoomPage now; if there is no room, a placeholder is shown
- SpaceHomePage is moved into RoomPage; This replaces the entire push/replace room/spacehome logic
- If the current room is a space, the space home is shown, otherwise the timeline
- The concept of "previous room" is removed entirely. If we're leaving the active room, the placeholder room page is shown
- When clicking on a space in the list, the space room list is switched and the space home page is shown
In short, these changes should (after some initial regressions) lead to a less crashy NeoChat :)
Make sure that messages are not marked as read when going back to the roomlist after entering a room when neochat is thin and only showing a single page
Fixes#642
