* increased the latency allowed between the server and executors. The server now also directly prints a warning to the shell when the connection with an executor is lost (for easier debugging)
* check_pipeline_status.py now also reports the number of runnable stages
* removed the ability to pickle a pipeline from the code. In large pipelines, pickling the stages can take many seconds to minutes. This severely slows down the communication between the server and executors, which in turn slows down processing overall. Also reduced the seppuku time to a minute to avoid idle time on the farms.
bumped version to 1.8, updated NEWS
Merge branch 'release-1.8' into develop
Merge branch 'develop' of https://github.com/mfriedel/pydpiper into develop

Conflicts:
	pydpiper/pipeline_executor.py