fixes #1030

It seems like handling the message in a blocking manner is a no-go. I
have no idea how to fix that, so just use a queued connection for now...
(ASAN does not cooperate and just hides the crash D:)

fixes #842

fixes #317

- 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.

In narrow view, a room can be selected even if the view currently only
shows the room list and the timeline is hidden.
This commit ensures that in this case, notifications are not suppressed.

* Add handles for window focus gained / focus lossed and connect to timer
* Clean up some of the PrivacyScreen.qml code
* Connect settings to PrivacyScreen visibility

Link opening only works on Linux for now.

See https://github.com/matrix-org/matrix-doc/pull/2312