Allow blocking invites from people you don't share a room with

Matrix currently has a significant moderation loophole, thanks to
invites. Right now, anyone can invite anyone to a room - and clients
like NeoChat will gladly display these rooms to them and even give you
a notification.

However, this creates a pretty easy attack since room names and avatars
are arbitrary and this is a known vector of harassment in the Matrix
community. There's currently no tools to block this server-side, so
let's try to improve the situation where we can.

This adds a new setting to the Security page, wherein it allows you to
block invites from people you don't share a room with. This prevents the
notification from appearing and NeoChat will attempt to leave the room
immediately.

Since this depends on MSC 2666 - a currently unstable feature - the
server may not support it and NeoChat will disable the setting in this
case.

src/CMakeLists.txt

@@ -134,6 +134,8 @@ add_library(neochat STATIC
     jobs/neochatdeletedevicejob.h
     jobs/neochatchangepasswordjob.cpp
     jobs/neochatchangepasswordjob.h
+    jobs/neochatgetcommonroomsjob.cpp
+    jobs/neochatgetcommonroomsjob.h
     mediasizehelper.cpp
     mediasizehelper.h
     eventhandler.cpp