When determining first file > start_time, catch StopIteration.

Was experiencing strange bug in this statement:
    i = next(filter(lambda i: files[i].time > start_time,range(len(files))))
Probably needs more looking into.
Localize times to dataset timezone. Improve error messages.

Add timezone to start, end time labels.
Improve time handling.

Add get_timezone, get_start_time, get_end_time methods.
Added validator for timezone.
Improve time handling. Support change in last dimension of a variable between files.

Catch TypeError when trying to parse time units "since" string.
Support page-backward, page-forward submits.
Added page-backward, page-forward submit buttons. Add timezone label.
Added more datasets.
DEEPWAVE datasets