cpp: PixelBuffer Add initial binary stream I/O support

Add all the interfaces and operators.  Actual implementation and tests
are currently stubbed out.
cpp: Implement forwarding methods in PixelBuffer
cpp: Add storage_order forwarding methods to PixelBuffer
cpp: Add initial stream read and write details to PixelBuffer
cpp: Add PixelBuffer stream I/O tests and fix ordering
cpp: PixelBuffer array() method will never return null
cpp: Add PixelBuffer data() method
cpp: Document new PixelBuffer methods
cpp: PixelProperties: Add pixelTypeFromBytes and pixelTypeFromBits

Also move some of the inline content of PixelProperties.h to
PixelProperties.cpp.
cpp: PixelBuffer: Add subsetting in the future
cpp: PixelProperties: Add isSigned, isFloating and isComplex functions
cpp: Document PixelProperties pixelTypeFrom*
cpp: PixelProperties, switch to isInteger for numeric_limits compatibility

Also add testcases and correct errors found.
cpp: PixelBuffer: Add virtual destructors and protect the PixelBufferBase constructor
do not insert acquisition dates by default unless from metadata
cpp: PixelBuffer: Add tests for dimension storage ordering
Prepend Maven central in the pluginRepositories block

This should decrease the burden on our artifactory to resolve external
dependencies in the Travis builds.
Prepend formats-common repositories with Maven Central (seralizer, xalan...)
Prepend autogen/pom.xml with Maven Central (velocity)
Prepend format-bsd/pom.xml repositories with Maven Central (perf4j)