263 active tasks

Fix #263. More specifically:
- Redefined `make_entry` as a member route and rewrote the relevant code in the controller (definition of action) and in the views (links to call the action).
- Fix the links to complete tasks in the /active_tasks page
- Allow task completion outside of shift
- Speed up the /active_tasks page by replacing a slow database query

It is built on top of #235 since I needed a working version of `make_entry` and I needed the task completion links in report_show page to work as well.
[See the compare](https://github.com/YaleSTC/shifts/compare/229_report_show...263_active_tasks?w=1)