Automate the date shown for the next event and auto load correct talk section template

- [x] automated date for the next event which is shown on home and talk page

- [ ] cleanup `dateService` and test so that it uses a `timeService` which then can be mocked instead of mocking the `getNow()` function directly on the service

- [ ] create folder `views/talks/` and then save templates like that:

/views/talks/2013_01.tpl.html
/views/talks/2013_03.tpl.html
/views/talks/default.tpl.html

This way we can make sure that we allway show the default.tpl.html for when we don't have created a new talk template for the next event yet.

Otherwise we would end up with a talk section that shows the next date but also still shows the old talks. That would be lame and confuses people.

It also gives us the possibility to view old talks either by directly manipulating the URL (e.g. #/talks/2013/03 or via a selectbox)