Use BinaryTree lists for gsSteps and gsTimelines

[ThomasBurleson]

Using unbalanced binary trees [instead of Arrays] to manage the order of gsSteps and gsTimelines will allow constructs such as ng-if, ng-repeat to be used and dynamically add/remove/sort the list of steps or child timelines.

See use of UbBT in /angular/messages.js

[ThomasBurleson]

Other resources:

https://github.com/andrewrjones/doubly-linked-list-js/blob/master/doubly-linked-list.js