Add support for events

:bomb: WIP

This PR is to add support for listing events on the 24pullrequest website. I am opening up the PR early to get some early direction and feedback.

### To do -

- [ ] Add event model and attributes
- [ ] Add map with events
- [ ] Restrict `event#new` and `event#edit` to logged in users
- [ ] Move all content into the locale files
- [ ] Add events link to the homepage
- [ ] Convert html to haml **requesting support**
- [ ] Add datetime picker

![image](https://cloud.githubusercontent.com/assets/1238468/4760789/cc23f92e-5af2-11e4-8160-be90cdb70e6a.png)

![image](https://cloud.githubusercontent.com/assets/1238468/4760809/f0ca6b46-5af2-11e4-833e-7dd0776987fe.png)

![image](https://cloud.githubusercontent.com/assets/1238468/4760817/fc0ac3a2-5af2-11e4-8035-8c49d56a3754.png)




Can you localise the notifications and move this to `config/local/en.yml` as w 24prs supports a number of languages. We can open an issue later and find people to do the translations as well.