[refactor] Reorganized tests (3m)
[refactor] Refactored the tests for Commit (7m)
[refactor] Moved Sprint out of Houston::Scheduler and into Houston (30m)
[skip] Allowed commits to mention ticket numbers and tasks (10m)
[feature] Added tasks to tickets (8h)

 - associated tasks with commits when mentioned
 - associated tasks with release
 - put tasks into sprints instead of tickets
 - tied effort to tasks instead of tickets
[skip] Smoothed out the sort experience for the Tickets view (1m)
[skip] Prevented hstores from being null (4m)
[feature] Added an API endpoint for listing and creating ticket tasks (1h)
[improvement] Displayed a second line on the Sprint burndown chart: progress committed (in addition to progress released) (20m)
[feature] Added an API endpoint for listing tasks in the current sprint (15m)
[skip] Added two helper scopes to Task (1m)