Suggested by:

Clazy: Use the static QFileInfo::exists() instead. It's documented to be faster.

I think old clang-format is just buggy in those cases, so we should
reenable those blocks, once everyone has 13 or up.

Either by accepting an invite or manually using /converttodm and revert
with /converttoroom.

fixes #317

Fixes messages in room flickering and being stuck

fixes #760
relates to #770
relates to #789

fixes #751

fixes #754

fixes #745

This ports the leave room dialog to QML, everywhere. There are now no differences between the various leave dialogs.

Showing the bootstrap state and showing there are unverified devices is
still missing.

Fixes for pasting images, especially under windows where the image mime type detection doesn't work as expected

- Fixes scrolling to an event not being reliable
- Adds new /goto command that can open URLs, go to events, or go to message indexes.
- Refactored ChatPage::handleMatrixUri() to contain the handling originally in Nheko::openLink(), and makes it return a boolean based on whether the URL was handled internally or not.