Added synchronization checks to all uses of mChildren and mPlugins

Signed-off-by: Jared Woolston <jwoolston@tenkiv.com>
Converted to CopyOnWriteArrayList

Converted mChildren, mPlugins, mFilters to Collections.synchronizedList
wrapped CopyOnWriteArrayList and removed all synchronized statements
related to these members in RajawaliRenderer.
Extended concurrency protection

Extended to include mLights and mChildren of BaseObject3D. Note that
this changes the method signature of addLights() in BaseObject3D,
AMaterial and AAdvancedMaterial.
Merge pull request #524 from Tenkiv/concurrency

Added synchronization checks to all uses of mChildren and mPlugins