Bug 485227: Content type calatog not updated after installing new plugin

Content-type extensions added or removed at runtime will trigger an
update of the content-type catalog to be ready to consume immediately
without restart.

Change-Id: I0543a8ad84be64b778fb956d7f4fbcd1d03de47a
Signed-off-by: Mickael Istria <mistria@redhat.com>