Make it easier to distinguish the events in the mission log

git-svn-id: svn://svn.icculus.org/fs2open@10278 387891d4-d844-0410-90c0-e4c51a9137d3
Allow training missions to also show mission goals.

git-svn-id: svn://svn.icculus.org/fs2open@10279 387891d4-d844-0410-90c0-e4c51a9137d3
Add support for replaying briefing and command briefing cutscenes. The go back a stage and go to first stage buttons will now count these as a briefing stage.

git-svn-id: svn://svn.icculus.org/fs2open@10280 387891d4-d844-0410-90c0-e4c51a9137d3