Bump up bootstrap css version to v3.2.0.

- Contents body 15px shifting bug when launch modal component is fixed in v3.2.0
  Refer: https://github.com/twbs/bootstrap/issues/9855
Update .gitignore to ignore MacOSX .DS_Store.
Merge pull request #6 from supistar/feature/bootstrap-css-update

Bump up bootstrap css version to v3.2.0.