[gitignore] Add main.css

Add main.css to be ignored by git. because main.css file is generate
from main.less file.
[less] Add bootstrap

add bootstrap basic styles.
- Core mixins
- Reset (normalize & print)
- Core Css (scaffolding, type, code, grid, tables, forms, buttons)
[less] add variables.less

copy paste default configuration by bootstrap.
[less] Remove grid.less

remove this file, because i dont wanna use a default boostrap css classes.
i want use mixins only.