CYB-59 Add a CSV export for points

 *  new activities_controller
 * exports CSV at `/activities.csv`
 * internationalized for column headers and activity names
 * removing old views from an earlier existence of an activity controller
 * now uses two Activity records; one for the liker, and one for the poster of the item liked
 * 2 new action types:  GetALike, GetADislike
 * 'MarkNeutral' is no longer a pseudo-status (it is gone)

[CYB-59 Add a CSV export for points](https://jira.ets.berkeley.edu/jira/browse/CYB-59)