Refactor (break up) rocksjni portal.h

[alanpaxton]

• We used some automatic help to parse rocksjni/portal.h and turn it into an individual class for each portal class rocksjni/portal/my_portal_class.h
• The portal classes were automatically created to include headers for the other portal.h classes they depend upon.
• We built a useful rocksjni/portal/common.h file to include the basic, initial set of portal classes that are used by almost all the others.
• We manually updated the #includes for the clients of portal classes to only include those class headers they actually need.