create method "get_stats_for_adaccount"

Create a method to get FB stats for an entire ad account.  Also fixes an unrelated bug in querying some endpoints based on start/end times.
Removed commented-out lines

I removed a couple commented-out lines of code that I forgot to delete before submitting the original Pull Request.
Update facebook.py
Merge pull request #29 from bpmason1/patch-3

create method "get_stats_for_adaccount"