Minerva friendly version of Special:Preferences

Display buttons and use sub pages for individual settings pages.
Only show sections which make sense in Minerva skin.

Currently doesn't support tabs injected by extensions e.g. Echo
Reset button doesn't make sense.
Let's iterate on this and refactor SpecialPreferences to support this
view.

Change-Id: I96a907233b8e0bd5776c744b78796a999933c48e
Merge "Minerva friendly version of Special:Preferences"