removed the FileBuffer from Nephele, and everything that uses it (Checkpointing, FileChannels)

Changed Nephele MemoryBuffer to wrap PACT MemorySegment instead of java.nio.ByteBuffer

Addressed Stephans comments
new memory segments methods

Remove checkpointing and envelope consumption logic

Signed-off-by: Robert Metzger <metzgerr@web.de>

Removed compression from nephele

Re-added tests.

Re-enabled JobManagerITCase with reduced logging verbosity.
Reduced test logging verbosity to only print warn messages.