fixes #122

The context is now configurable for annis3 again via annis-service.properties
or a specific corpus.properties  file in the relAnnis/ExtData folder.

Note, that the max left or max right context from a custom corpus.properties
file is overwritten by the values defined in the annis-service.properties file,
when they are bigger:

min(corpus.max-left-context, annis-service.max-left-context)
min(corpus.max-right-context, annis-service.max-right-context)