Using .less instead of .css

I have rewrite the styles.css into different .less files:

* styles.less - General .less file with the most of the code
* definitions.less - Currently, all the color definitions, to easily change the color
* mixins.less - Functions to add special css-rules (like border-radius,...) as one command

To generate the styles.css, the command ```make styles``` has to be called. (After updating the .less-files). To do this, the command  ```lessc ``` is required (available in the package ```node-less```)

Advantages:
* easier Customisation
* output is compressed
* more understandable code (variables, using comments, which doesn't blowing up the style.css,...)

Todo:

call ```make styles``` when build the project

In the style itself, only one little change has affected, to display the download-result text (in german) without line-break.