horizontal collapse with width class

[plong0]

add width class to a collapse item to have it collapse horizontally.
You will probably want to add a <div class="content">...</div> wrapper inside your collapse item.
My modifications use this to avoid wrapping when expanding/contracting.

[plong0]

Started working on a configurable ng-collapse directive at: https://github.com/plong0/angular-collapse

[icfantv]

@plong0 please update/rebase/squash this with the appropriate functional test(s) added.

[wesleycho]

Closing as outdated - feel free to open a new PR implementing this feature based on current master