Detect chemical table files: Add them to MIME listings

Detect chemical table files: Add them to MIME listings

Adding mol, sdf, rxn, rd and rg file types to mime.types and mime.info
map to make them known to MediaWiki by default.

PHP's own module fileinfo module is not capable detecting Chemical
table files. Instead, they are reported as text/plain.

MediaHandlers can be attached by MIME type only. That's why these
changes are required for [[Extension:MolHandler]] to work.

Change-Id: I017507e4a950b3ce4e6576d12217cd42a337bad6