Adding the allowing of image map to htmlpurifier (Bug #1354286)

To test:
1) add an image map to a page
2) you may also need to add:
$config->set('Cache.DefinitionImpl', null);
to line 3252 of the lib/web.php page so the htmlpurifier cache is
ignored

Change-Id: I19ce97394ab52aea300cbf7c6b2c458ec7dcf5b9
Signed-off-by: Robert Lyon <robertl@catalyst.net.nz>
Merge "Adding the allowing of image map to htmlpurifier (Bug #1354286)"