Change beam charging light sequence to be 4-phase.

This now goes 1,2,3,4-blinking rather than 1,2,3,4,4-blinking so it is
more obvious when the beams are charged, to prevent people trying to
fire "full" banks that have not reached blink phase yet.
Merge pull request #2 from Jonty/master

Change beam charging light sequence to be 4-phase.