Make more classes package-private

[rheitjoh]

Done

• Made supersingular and Barreto-Naehrig bilinear group stuff package-private
• Add BasicBilinearGroup versions of the supersingular and BN pairings.
• Made lazy group stuff package-private
• Made representation handler stuff package-private and moved package up a level
• Adjusted recreateRepresentable to make constructors of package-private classes accessible via reflection
• Adjusted StandaloneReprTest to not collect package-private classes for testing
• Made ring group impl stuff package-private
• Added inv and neg cost estimation to remaining Ring implementations

TODO

• Should probably have another look over the javadoc