Expose game paused to Lua; disable bulletin board when paused

Work towards closing #2732.

One remaining task is to give some visual cue to the user that the
bulletin board is no longer clickable.

Another could be to wrap the 'disabled on paused' semantic into
something more reusable for other UI. I think this is out of scope for
Agree with parentheses.

I don't see any mistake in the logic - if SetTimeAccel is called with paused when the state is not paused, we should emit paused. If SetTimeAccel is called with any other value when paused, we should emit resumed.

If there are multiple calls to SetTimeAccel with first paused, then non-paused, then paused... then I can see a problem. I don't see that happening in UpdateTimeAccel.

Calling SetTimeAccel repeatedly with non-paused values will not produce lots of signals. Similarly, calling SetTimeAccel with lots of pause values will not produce lots of signals. That's the intent of this change - if I have my logic wrong, then perhaps that's not the effect, but I can't see where I'm wrong.