This makes them less annoying when scrolling or accessing the popup
menu.

See also #860

This breaks the vertical-centeredness on the close button.

fixes #683
relates to #571

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

As well as selecting more join rules.

Also fixes some issues where nested transactions will poison the
verification cache.

Room Directory UI for exploring and joining public rooms. V1: simplistic server + network facilities

Also fix a lot of warnings.