Update to rails 4.1

I noticed the PR from @chunlea and used parts of his code to upgrade huginn to rails 4.1

Here what is done so far:

* Upgrade rails and the most essential gems
* Used a fresh rails 4.1 app as boilerplate to update the environment configurations
* Updated the devise initializer based on a fresh installation
* Tests pass
* The application boots and seems to work with no problems

What still needs to be done, or discussed:
- [ ] Further check for gem updates and test them (Gemnasium?)
- [ ] Verify everything runs in production
- [ ] Verify the twitter-stream actually works
- [ ] Check the geokit related agents (did update geokit-rails but not geokit, which currently is two minor versions behind)
- [ ] Update the stating environment configuration (left it as it was because it looked out of dated compared to the 3.2 production environment)
- [ ]  Decide whether or not to migrate to strong parameters (would be some work but should pay off in future updates)

The only thing needed to be done manually to update is to set the `DEVISE_SECRET_TOKEN` in `.env`