Adding Working Periods menu

This menu should allow users to set their own working times to help
automatically pause their issues. See the README for more info.
Fixing small Working Period bug
Minor Working Periods update
Adding comments to working period virtual attributes
Adding default option for time zones
Fixing time comparison bug

Comparing Time objects directly to check for working period overlap does
not work if working periods created on different dates (e.g. "9am 10th
Oct" will be greater than "10am 9th Oct". Times are now parsed to ignore
dates and only compare times of day.
Merge pull request #40 from dannybutler/master

Adding Working Periods menu