Goals model, migration and first tests.
sat_on_date?, rating and days_where_goal_met
goal#to_s and tests for goal helpers
goal#rating_colour to grade progress
Goal factory and trait to simplify tests
Remove superfluous db fields
Fixed goals (30 min per day), tests, and helper methods.
Added methods to process sit stats from a date range: single query.
Allow fixed goals to specify day count and mins per day. Refactoring.
Remove more db fields in favour of one virtual attribute: #completed?
Clear up conditional
Merge pull request #135 from danbartlett/goals-backend

Goals backend. Fixes #129