Some history file additional functionality.

[dabail10]

I have been asked to add the capability to for restart history files. This means that the model would write "interim" average files, so that if say the model stops in the middle of the month then one can restart the monthly history averaging exactly. It is fairly complicated, but should be straightforward.

Another functionality is to change some of the time metadata names. This might need a CESMCOUPLED ifdef.

Finally, adding the option to have the timestamp of the history files to be the middle of the averaging period instead of the end.