[READY] Implement tags overview

![screen shot 2014-08-27 at 16 06 39](https://cloud.githubusercontent.com/assets/642544/4060879/7f4d9ba4-2df3-11e4-92ed-adb32dd9dfed.png)

In this overview you can see the hours spent on a certain tag. You see the hours on that tag per user and per project. Also all the entries for that tag are listed, your entries in there can be edited. All the tags in the application are clickable now.

I also renamed the javascript charts file from project to charts since the charts are used in multiple places. I also moved some css to application because it was used in more places. Last of all i updated the annotation.
Specifically this: https://github.com/DefactoSoftware/Hours/blob/time-series/app/models/time_series.rb

You can throw in any range of entries and you can get a time series from that object, I think we could do the same thing with the other charts that we reuse ^^