Adding ability for owner/admins to remove volunteers from tasks.

Task Owners and admins have the ability to remove volunteers from
tasks. This is done via the task edit screen.

Fixes #411
Moving volunteer removal outside the task edit form.

Moved the volunteer removal component off of the task edit form
and into a box like it appears in the project owner page.

Fixes #411
Merge pull request #423 from DavidEBest/devel-removevol

Adding ability for owner/admins to remove volunteers from tasks.