Display banner for first newperiod

[michaeljyeates]

When the DAC is locked but newperiod has not been called, display a message to anyone logged in to prompt them to call newperiod.

It should ask for a message to use and then submit the action, it should be prepared to handle the error where newperiod is not due (meaning someone else triggered it)

Once the first newperiod has been called, the automated system will call it when due.

[piecesnbits]

memo todo: language strings