Prepare patternlab

- [x] Remove default demo CSS
- [x] Set the basic `.scss` files #12 
- [x] Set the SASS build system #8 
- [x] Set a *watch* task in *Grunt* #13 
- [x] Refactor `.gitignore`
- [x] Remove demo JavaScripts #9 
- [x] Remove unused patterns #15 
- [x] Remove unused images #10 
- [x] Remove fonts #11