Modularization / Sass-Variables Style

As we decided to modularize the code even more, especially some of the Sass values it is now in question how to manage this.

Version 1: As of now we have a `_variables.scss` file containing all var definitions for Sass. This is nice to have all in one place but might annoy users because they need to reverse-search and always switch to the separate file.

Version 2: We could define variables on top of each Sass-module-file. This would improve usage of variables in _base.scss drastically but as we still would need global var definitions for e.g. custom colors, we should keep `_variables.scss` also.

What do you think? Does version 2 make sense or not?