Minor refactor: avoid some .data() overhead and remove a TODO

[valerio-bozzolan]

Here you are two minor refactor:

• https://github.com/ludo/jquery-treetable/commit/f31d4c3c1567a554b0609a407946f3a3006bb117: In the methods loadBranch and move there were multiple calls to jQuery's .data('treetable').
• https://github.com/ludo/jquery-treetable/commit/760fabee3a9273778aa28d02be9e5ecd4395a36e: The fact that now everything in the method loadBranch is encapsulated in a jQuery object allow to pass structures made using jQuery (e.g. $( '<tr>' ).append ... ) so it's a feature and it's a better approach over $.parseHTML.

Thank you!