add support for an external message catalog

Instead of having the messages inline, we should do them in the
yaml file so that changing the UX for the bot reporting isn't a
code change.

Depends-On: I9208123a4cb3be02c272cd8a6eba460f4130a960

Change-Id: I8fdb07f9964f616addba6e8f25e5bd9de27d077a
Merge "add support for an external message catalog"