Update examples and lessons

* have less examples
* have smaller lessons

Examples should be a reference implementation instead of being a proof of concept. Many people use it as a reference whereas it is not optimal.

Examples:
* upload
* quadview
* volume rendering
* widget

Locate the upload, quadview, volume rendering, and widget examples, along with the lessons that describe them. Review each as a reference implementation and identify how the examples and lessons can be reduced while remaining useful. Done means the listed examples are smaller, more focused, and suitable as optimal references rather than proofs of concept.

Written by the indexing model from the issue text.