Update package to Bootstrap 3 with x-editable 1.5.1

Given that Bootstrap 2 is no longer really supported, and that it will probably be demoted from core by Meteor 1.0, would you take a PR to update this to Bootstrap 3? The BS3 package on atmosphere (https://atmospherejs.com/package/bootstrap-3) has almost 10k downloads. I would add the following:

* update to x-editable 1.5.1 BS3 build
* update other files now supported in 1.5.1
* add dependency on `bootstrap-3` package

@gregorynicholas also seems to have updated to the latest version in his branch but it doesn't look like something that could be merged back in here.