work on activity model.
made activity model specs pass.
work on activity callbacks.
activity actor can now take both User and String/ObjectId.
have note destroy mutation take updater.
merged from master.
added callbacks to project model.
associate activity with recipient's parents.
search for all activity for project.
work on a sentence for displaying an activity.
display activity sentence in project header.
fairly rudimentary way to view activity.
Merge pull request #108 from noted/28-activity

Show activity within a project