Improving mission debug menu

[ghost]

Actually it's quite useful, but I think it misses something:

• option to stop actual mission,
• changes are introduced when we exit debug menu, so maybe some live status info text "mission is in progress?"
• using https://github.com/rwengine/openrw/wiki/Mission-tracker as pattern, maybe mission from one person should be written using the same color?
• freeze mission timer

[ghost]

It terminates already running mission

[ghost]

Yeah, but sometimes there's a need to unlock camera and make a cleanup.