Adding basic functionality

MediaHandler for rendering Chemical table files (*.mol and
*.rxn for now) using either indigo-depict or openbabel.

Of note: When testing, make sure your MediaWiki installation detects MOL
and RXN files properly as such by applying Icf9eec10bec7c to your core.
Also make sure that when using MySQL, you add "chemical" major MIME type
to the image tables by applying Ic45dc1bce796a04.

Change-Id: Iac7b7c429eb9033dc7932e1f8cb77c74bbcce892