activity feed styling improvements (more links and better spacing)

Also added add_user_to_project to template
added $model->exists($id) method on MapperModel
added method readListAsModels() on MapperListModel
activityDto refactor wip
fixed up readListAsModels() on MongoMapper
finished refactoring of ActivityDto and related tests
Merge branch 'master' into feature/activityfeed

Conflicts:
	src/css/sf.css
fixed reset_db.php
fixed up dto
fixed MongoDecoder DateTime problem and added test
WIP on comments: Adding comments works, just once

Adding the first comment for any given answer works. Adding the second
comment fails. But this is progress over what we had before, so I'll
check it in, then start working on making second (and subsequent)
comments work as well.
fixed timestamp display
activity filter working
activity dto sort fix
Merge branch 'master' into feature/activityfeed
Merge branch 'master' into feature/questiondto
Fix #38: Mongo decode of id picks up incorrect id.
wip: rights for projects and project.
rights: questions page
rights: QuestionDto