Update VGL to lastest version

Change-Id: Ic9b646c0c4232ce77c5edf40fd117f78652e7f0c
vtkWeb: Refactor fetchObject(..) to use cached objects

Refactor fetchObject(..) to use a more straight forward cache
mechanisum. Moving much of the logic out of vtkReader.js.

Change-Id: Ib878dd70cb0a9427ba2015159b0ed34db0bc451f