Refactors Transition Helpers into Separate File and Moves Methods into
CollapsibleBody

Move the transition helpers into a separate file. Update gulpfile.js
to concatenate new file. Update all helper function calls.

This allowed me to move methods into CollapsibleBody. Moved over all
methods that work on CollapsibleBody DOM node.
Fallback for Transitions

Adds checks in all Transition helper methods to return if transitions
are not supported so that we don't have to wrap every call with an
if statement.

If transitions are not supported, call `this.finsihOpen()` and
`this.finishClose()` at the appropriate location.