WIP - adding monthly response class
Add month timeseries
Add response class for monthly grouped data
Make PeriodData class work for months and weeks
Add ability to group by months to query object
Rename method for doing period grouping
PEP8
Set _month_start_at on incoming event data.

@gtrogers
@robyoung
Merge branch 'master' into monthly_data_grouping

Need the fix to database migrations from master
Add migration for monthly data
Make migration logging more verbose
Change validation to allow period=month
Include all data in monthly response

Was previously only adding the datetime infromation to the response
Add validation for month queries
PEP8 fix
Add feature tests for month grouping
Merge pull request #77 from alphagov/monthly_data_grouping

Monthly data grouping