Replace growl with pnotify

Re: #2924

This is a preliminary code review pull request. There are a few issues with the code as-is:

# Alerts do not have a close 'X' icon, but you can click them to get rid of them (this behavior can be changed).
# Alerts stay on page longer than the growl alerts did. 
# Code has not been run through the unit test suite because I'm experiencing issues running the tests (selenium won't start).
# Pnotify's facility to redisplay either the most recent or all the alerts since page load is obscured by the toolbar (see the upper right corner of http://sciactive.com/pnotify/ for this in action). I believe someone better versed in interface design would probably want to tackle this, especially since the default interface uses the same chevron as the toolbar expander.

I decided to submit this pull request because I think someone else can probably run with this, while I try to tackle issues with the vagrant image.