See #469

* making userName_ an AbstractButton should make it play nicely with the ListView

* make Avatar an AbstractButton

* make userName_ in Reply.qml an AbstractButton

* use alias for avatar background color and fix margin of username in reply

Mobile room directory

support for hidden read receipts

WebRTCSession: avoid deprecated 'gst_element_get_request_pad'

It seems that you need to manually destroy created objects... Great...

fixes #898

* add sendernames to state events

* Center state events and make them less tiny

Fix timeline scrollbar

use shortcode as a fallback for custom emote title

Make UserSettingsPage fit on a phone screen

That way we can autohide the scollbar if needed, it should fix some
jumping issues, it makes it possible to flick on mobile, etc.

Some related bugs:

https://bugreports.qt.io/browse/QTBUG-75223
https://bugreports.qt.io/browse/QTBUG-44902

Make search usable on mobile

Make hover highlight fill the full width of the timeline

Rows in the message bubble design are only as wide as the bubbles. This
lead to invisible hover highlight. Now it's consistent.

fixes #941

Place metadata next to content if there is space