Update Bootstrap CSS source and relevant tests. Closes #36

This PR request removes reference to old Bootstrap Bower package resulting in version 2.3.* being used for `css` option. It also reword test for `less` option to use `components-bootstrap` as name of package being tested - which cleans wording of tests for each CSS version supported (css/sass/less/stylus). Now the name of options, tests and packages are consistent with Bower names.
```
- use official Bootstrap Bower package
- update installation test for Bootstrap css version
- update wording of Bootstrap less component test
```
test:
```bash
Bootstrap generator test
    ✓ the generator can be required without throwing 
    ✓ installs bootstrap 
    ✓ installs sass-bootstrap 
    ✓ installs components-bootstrap 
    ✓ installs bootstrap-stylus 


  5 passing (35ms)
```
After this change using `css` option with generator:
```bash
yo bootstrap
? In what format would you like the Bootstrap stylesheets? css
bower cached        git://github.com/twbs/bootstrap.git#3.3.1
bower validate      3.3.1 against git://github.com/twbs/bootstrap.git#*
bower cached        git://github.com/jquery/jquery.git#2.1.1
bower validate      2.1.1 against git://github.com/jquery/jquery.git#>= 1.9.1
bower install       bootstrap#3.3.1
bower install       jquery#2.1.1
bower no-json       No bower.json file to save to, use bower init to create one

bootstrap#3.3.1 bower_components/bootstrap
└── jquery#2.1.1

jquery#2.1.1 bower_components/jquery  
```