improve packaging of JSON support in uimaj

Based on good suggestions from Richard, change the packaging for the JSON support as follows:
1) Move its package / code to the main uimaj node in svn.
2) delete the uimaj-json project in addons
3) make a profile that is enabled by default to include the uimaj-json artifact in the uimaj build, both to build and to include in the binary assembly (with the jackson-core jar).
4) document updates, including how to exclude uimaj-json from the build and the binaries, if wanted.