TCK: review follow ups and additional tests / blackbox tests
* Make spec rules linkable (#2.13) and use links in TCK
* Verified 1-element-publishers are testable with TCK (skips unsupported tests)
+ moved 3.2 from subscriber tests to publisher tests
+ moved 3.4 to publisher
+ moved 3.6 spec to Publisher
+ check rule 3.3, assuming publisher breaks the reccursion
+ Splitting subscriber whitebox / blackbox tests
+ both got verifications of rule 2.3
+ whitebox is the previous impl
+ blackbox is tests which work without any additional probes
  it mostly wrapps the subscriber in order to check things
+ better 2.10 verification in blackbox
+ test was testing onComplete instead of onError like it should
+ better blackbox tests for 2.9
+ more java-doc style java-docs (added {@link}s)
+ minor cleanups and refactors to make BlackboxProxy more understandable

Awaiting either more feedback or maybe an initial merge so we can
continue working on the TCK from there on?