Added colour option and improved tracking

Added a colour choice making it independent from physgun colour. In
tracking mode the beeps are more dynamic - the closer you are pointing
to it the faster it beeps until you're actually pointing at it where it
will beep 4 times a second (0.25 delay between each beep). All TARDIS
interior controls (including monitor/door) can be now be used just as if
you were pressing your use key on them.