sample code in tutorials should match the SDK's "JME3 Tests" project template

See https://github.com/jMonkeyEngine/jmonkeyengine/issues/1124, filed by @nav9. They missed part about "All example code is included in the jMonkeyEngine SDK" and tried copy-pasting code from the beginner tutorials. That ought to work, but it didn't. They mentioned 2 sorts of problems:

1. small errors in the code
2. non-breaking space characters

I assume the SDK build process somehow copies the Java code in the "JME3 Tests" project template from the jme3-examples sub-project of the Engine, so that's an important piece of this issue. Whenever changes are made the tutorial code, it's vital to replicate those changes in jme3-examples. This will ensure that the code actually compiles.

Similarly, it's important that changes to certain jme3-examples classes (the ones used in the wiki) get reflected in the wiki. Perhaps we should add prominent reminders to the Java code.

A related topic at the Forum:
https://hub.jmonkeyengine.org/t/hellocollision-will-need-update-for-3-2/39730/7

Start by reading the beginner tutorials, the jme3-examples sub-project, and the SDK’s "JME3 Tests" project template to compare their Java samples. Check for the reported code errors and non-breaking spaces, then review the wiki classes used by the tutorials. Done means the tutorial and template code stays synchronized and compiles in the SDK context.