Remove img_float.

"float" is not a valid option, although it has been accepted as such
by Parsoid for a longish time.  It does not appear in the PHP parser
(Parser.php) nor in the localization information for image option
names.

Bug: 62500
Change-Id: Ia38c4473c0e6cadb6d136def47df6641fe974ec1
Parse and round-trip even invalid image options.

We now preserve information about invalid options/extra captions in
data-parsoid, allowing them to be round-tripped cleanly.  To avoid
propagating broken wikitext, if the image options have been changed we
discard all the 'bogus' options/captions.

Bug: 62500
Change-Id: I6d94c908f39c8f9e7b494e8ef72db726c0ce15e3
Merge "Remove img_float."
Merge "Parse and round-trip even invalid image options."