Adds methods to fetch timezones as timezone objects.
Fixes a number of things in the simple sleep entry.

Including:
*make a better form for sleeps, that does the validation and conversion
to datetimes correctly, including timezone checking and overlap checking
(no need for an override as that's actually impossible now that we use
timezones)
*continues to work with 12/24 hour time
*URL is now /sleep/simple/ because it's nicer
*Now linked from /mysleep/

In general, anything that can use sleep.forms.SleepForm should, since it
will handle validation and timezones correctly.  At some point we should
change the grid interface to use that.
Makes SleepForm raise a ValidationError instead of a 500 for misformatted dates.
Fixing bugs
Increase max length on SleepForm
Merge branch 'master' of github.com:benjaminjkraft/zscore
Fixes initial values in edit sleep.
Adds message about emailing us to bulk-update to mysleep.
Fixes typo that was hiding success message on editSleep.
Merge branch 'wakeup'
Makes editSleep always post to current page rather than always to /sleep/simple/.
Merge branch 'master' of github.com:benjaminjkraft/zscore
User - > Sleeper
Merge branch 'master' of https://github.com/sleepers-anonymous/zscore
Uses a better example than today in the format error in editSleep.
Merge branch 'master' of github.com:benjaminjkraft/zscore
Import all the errors
Merge branch 'master' of https://github.com/sleepers-anonymous/zscore
Fix to validation errors in editSleep, dammit django bugs.
Merge branch 'master' of github.com:benjaminjkraft/zscore