-added show/hide methods to baseHelper
- refactored DimensionsHelper:
 * added attach/detach methods so that it behaves somewhat
similarly to three.js transform controls
 * it is now not meant to be added as a child of the object
whose dimensions it displays, and can be kept in a seperate scene
 * refactored the code accordingly to the points above (ie
moved most of the code from the constructor to the "attach"
method)
- updated DimensionsHelper.js
 * modified bounding box computation so that no corner cases can arise
 * removed some clutter & console.logs
- minor cleanup of SizeHelper (removed clutter, console.logs)