This reverts commit ec799d44.

This reverts commit b34dd86e.

This reverts commit 80f4f133.

Also added translation calls for some UI messages.

The existing logic for filtering out MISSION* messages that don't apply to this instance of QGC wasn't clear and exactly correct. This refactoring reorganizes the code to be more clear and makes it explicit when the messages should be ignored by this instance of QGC.
Additionally a few more status messages are translated to be helpful to our non-English speaking devs/users.