Make buildjs.sh script automatically update JS SHA.

Having to manually update the SHA in views.py every time
you recompiled the javascript files was very tedious.
Load thread if requested thread isn't loaded yet.

This builds on https://github.com/edx-solutions/xblock-discussion/pull/29.

If the thread that was requested directly through the URL isn't loaded yet,
issue a request to load and display it.
Merge pull request #30 from mtyaka/thread-load-fix

Load thread if requested thread isn't loaded yet.