implemented answer and judging period

- I had to upgrade angular-strap to 2.0.5 from 2.0.3 to fix a bug
when using the datepicker and timepicker.
- Due to upgrade of angular-strap, I've also install Bootstrap 2.3.0
- The time periods are printed on the question view
- a hybrid_property is also created to check whether the question is
available. However it cannot be used in query filter.
Hide buttons when Answer/Judging periods are not in session

Right now if for example the answer period is not in session,
the button is hidden from the user and the api will reject any
create/edit requests. Similarly for the judging action and the
judgement period
extend availability period of questions to "forever"

Modified design to have the availability of questions to never end.
This allows users to go back to view answers and comments after the
judging period
Implemented instructors' answers (appear after judgement period)

Now, instructors can submit an answer that would not appear for the
students until after the judgement period OR immediately if no dates
are set. The answers will by default appear on the very top with the
label "Instructor's Answer" or "Teaching Assistant's Answer".

Modifications have also bee made to the question interface for
instructors. I have now allowed instructors to submit and edit
their answers any time (instead of just within the answer period).
However judgement is still only allowed during the judging period
for everybody (including instructors)
Merged question-view-partial