RevertToDefaultButton
BackButton
Default
HoverTarget
Felt quite convoluted to follow. Have just duplicated the single shared line instead.
SidebarIconButton
This also - Renames TextAwesome to SpriteIcon. - Removes the default size of "20" from SpriteIcon (now defaults to the underlying texture size).
Depends on https://github.com/ppy/osu-framework/pull/837