[CLC-1448] Filter functionality for activities

JIRA: https://jira.media.berkeley.edu/jira/browse/CLC-1448

Second part of the pull that handles the filter functionality, done in js. For the front-end devs, I probably did a big no-no with the select by using ng-repeat [select docs] (http://docs.angularjs.org/api/ng.directive:select) and [warning](http://stackoverflow.com/questions/13180797/ng-model-attribute-in-angularjs), but there's the annoying horizontal bar that ended up triggering this. I figured it might be acceptable since the select might not stay in for that long.

Second bonus piece, you can filter on both source and emitter as was in the design, though the jira only says source.