Make the 'full size' button optional

Transform MediaSizeWidget's 'full size' button to appear only as an
optional configuration option. This is mainly used in the new correction
related to MediaEditoDialog type and default size change at
https://gerrit.wikimedia.org/r/#/c/115939/

Change-Id: Ie18e2e371f18f5e8ab37ad27810ff11e5ee92d32
Merge "Make the 'full size' button optional"