Improve font/language handling in multiwiki collections.

Ensure that the table of contents is always in the language of the
collection as a whole, even if individual articles are in different
languages.  This avoids ping-ponging between LTR and RTL styles for
chapter numbers, etc.

Also reset language when entering figure environments, and use
\itshape and \emph instead of \it and \textit (respectively).

Change-Id: I8dcc7ad8571a47a23b9e0e1e9c7d66dd07f039c4