[Engine-Campfire] Support file upload events
[Engine-Campfire] Add an /uploads command

This commands lists the last five uploads to a particular room. This
is the same information as is available in the web interface.
[Engine-Campfire] Refactor to make it easier on translators

The piece-by-piece building of actions makes the translator's job
harder than it already is and makes the sentences forced even in the
original.
Merge pull request #17 from carlosmn/uploads