Extending the "Join Task" Button

For some projects where only one user is needed to perform a task, the
wording "Claim" can be more intuitive than "Join Task". This change
checks to see whether the number of accepted people on a task is equal
to zero, while the number of needed people is equal to one. If this is
the case, then the text on the Join Task button will be "Claim".

For all other cases, the wording on the task will be "Join Task"
Adding new sections to the Task page

This update will add two new sections to the "Task" page:

1) "Unclaimed Tasks" - These are all the open tasks that would normally
show in the "More Tasks" section, that have 0 participants signed up for
the task. If you are the leader of a task but there are 0 participants,
the task will not show in this section (it will continue to show in the
"Your Tasks" section)

2)"Closed Tasks" - All of the closed tasks for a project will show in
this section.

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Change to existing behavior (1 change):

1) Closed tasks will no longer show in the "More Tasks" section. They
will now show in the "Closed Tasks" section
Merge pull request #41 from kluther/Joe

Extending the "Join Task" Button