checkbox(-group), radio(-group): css, refactoring

close #508 
By default radio and checkboxes inside their groups are divided by line break.
Line view (with proper margins) realized in `type_line` modifier.

![2014-05-29_1832](https://cloud.githubusercontent.com/assets/521273/3118639/245576a0-e73e-11e3-8f39-aa230b7cfda3.png)