Added Milestone editing 

This is a PR against the `rednovalabs-feature-create-milestone` since I am unable to add it on to the previous PR since the branch changed.

This PR covers the following items
* Added `description` and `due_on` to milestone creation
* Added Bootstrap Datepicker plugin for selecting a date
* Added `gear` icon to milestone column header for editing a milestone
* Added `title` tooltip to collapsed milestone in order to see the milestone name on hover

Items that are still incomplete
* When editing a milestone, the `due_on` date needs to be formatted without the time
* `gear` icon needs to be removed from the `No Milestone` column
* Does `lib/api.rb` still need to exist? When adding the PR, it is noted as a new file, but I didn't create it...
* Update milestone name after editing a milestone (`forceRedraw' somehow?)