Recreated keyframe example: The same functionality, but only 7% animation code

RectAreaLightHelper: Removed unused variables

RectAreaLight: cleanup and refactoring

Update ISSUE_TEMPLATE.md

Update LOD.html

error in example

Set LightHelper color equal to the light color

Blender exporter improve

Simplified RectAreaLightHelper

Examples: Fix webvr_rollercoaster

wwobjloader2 docs and code enhancements

Code related changes:
- Validator and its functions replace all Boolean calls. It is included in THREE.OBJLoader2.
- Versions are now defined inside OBJLoader2 and WWOBJLoader2.
- Static OBJLoader2._getValidator and OBJLoader2_buildWebWorkerCode are reached via prototype of OBJLoader2. Instance of OBJLoader2 is no longer created.

Bugfix in webgl_loader_obj2_ww_parallels:
- Fixed "Run Queue" started new run before first was completed.
- Replaced Boolean with Validator

Update Useful-links.html

Removed broken links

- http://threejsdoc.appspot.com/doc/index.html is broken 
- three.js tutorial in german is deprecated

Fix blender exporter tests

Code related changes

THREE.OBJLoader2.WWOBJLoader2:
- Function _receiveWorkerMessage now uses a meshDescription that allows to override material or bufferGeometry or to completely disregard the mesh. THREE.OBJLoader2.WWOBJLoader2.LoadedMeshUserOverride was introduced for this.
- Allow usage of multiple callbacks per callback type
- THREE.OBJLoader2.WWOBJLoader2.PrepDataArrayBuffer and THREE.OBJLoader2.WWOBJLoader2.PrepDataFile require less mandatory parameters. Setters are introduced to handle optional things

THREE.OBJLoader2.WWOBJLoader2Director:
- Added per queue object callbacks
- Global callbacks in prepareWorkers will be specified with new object OBJLoader2.WWOBJLoader2.PrepDataCallbacks. This object is also used in both PrepData objects for defining extra per model callbacks in addition to the global ones
- Callbacks will be reset and reassigned for every run

All:
- Improve code quality, especially, replaced != or == with Boolean() or ! Boolean() where applicable
- Improve logging and comments