changed visibility of constructors in diverse abstract types to public
because all existing implementations require them as public constructors
made ARGBType non-final as we're extending it downstream
loosened generic parameters for NativeImg in ARGBType in line with Tobias'
recent changes for RealTypes
commented ARGBType and GenericShortType
split abstract base class off VolatileNumericType as with VolatileRealType
Merge branch 'master' into janelia1

Conflicts:
	core/src/main/java/net/imglib2/type/numeric/ARGBType.java
	core/src/main/java/net/imglib2/type/numeric/integer/GenericByteType.java
	core/src/main/java/net/imglib2/type/numeric/integer/GenericShortType.java
	core/src/main/java/net/imglib2/type/volatiles/VolatileNumericType.java