Added viewlet to colorize special pages as dev, test, ...

To set a color for your system, just add in your buildout in the instance section:
```
environment-vars +=
    gever_colorization MY_COLOR
```
MY_COLOR can be the here defined colors (now they are 'green', 'red' and 'yellow':
https://github.com/4teamwork/opengever.core/blob/48e50d6d141d7a1f24f7dac70b7ae68ecc38a05f/opengever/base/viewlets/colorization.py#L6

@phgross Please feel free to complete this list if you misses some colors.

I've chosen a simple border around the whole page to identify the special systems, so it will work, even if you have a customized theme configuration:
![bildschirmfoto 2014-07-03 um 16 08 52](https://cloud.githubusercontent.com/assets/157533/3470642/5cdaf402-02bc-11e4-9e71-ec7c4e11be5e.png)