Solr search capability

First attempt at issue #9. Adds new indexing capability on create/update/delete, includes embedded Solr and test cases/data. Rebased from master to keep things in sync.
Yes, it makes sense, my point is to keep controller as clean as possible, only doing its job: calling models and retrieving responses.
Other way to do that would be making a QuestionDAO#load method that receives a `List<Long> ids` and returns `List<Question>` :)