Make prefixes for radio chanels consistent between jobs.

[myeffort]

Now I'm pretty sure I will never stop mistaking heads channel for engineering channel whenever I'm CE, or engineering channel for no cha[public channel whenever I play QM or mechanic.

Make it so that heads can speak on heads channel via :h, engineering with :e, research with :r, medical with :m and in special cases (i.e. multi-frequency and operatives headsets, :h traditionally corresponds to special frequency).