Uses GetContainingInputManager instead, as per framework changes.
Also removes an unnecessary secondary list of SidebarButtons by using generic containers.
This also - Renames TextAwesome to SpriteIcon. - Removes the default size of "20" from SpriteIcon (now defaults to the underlying texture size).
Fixes a potential threading issue when updating Text.
Posts can be triggered by Logger.Log events which are not guaranteed to be on the update thread.
Also adds an option to delete all beatmaps for testing purposes.