Remove grunt-bower-task, replace with grunt-shell

Addresses GH #7 - grunt-bower-task was choking when trying to install
jasmine. Now instead of using grunt-bower-task we use grunt-shell and
add bower itself as a dev dependency, then simply run `bower install`.
Merge pull request #8 from refinery29/gh-7-fix-bower-install-task

Remove grunt-bower-task, replace with grunt-shell

fix #7