Make property names customizable (beeminder-properties)

- Remove beeminder-request-data: No longer used.
- New customizable option beeminder-properties.
- beeminder-on-org-task-completed: Use beeminder-properties.
- beeminder-refresh-goal: Use beeminder-properties.
- beeminder-my-goals-org: Schedule, and use beeminder-properties.
Merge branch 'tweak-for-regular-use'

Conflicts:
	beeminder.el