CC-4999: Do silan analysis quietly in the background

-set silan nice level to 19
Add versioned dependency on Silan 0.3.0 [#CC-5006]
CC-5012:
remove all shell=True commands for subprocess calls

-fixed
Merge branch '2.3.x' of dev.sourcefabric.org:airtime into 2.3.x
minor fixes

-don't show print subprocess commands to py-interpreter.log
Merge branch '2.3.x' into devel
Merge branch 'devel' of dev.sourcefabric.org:airtime into devel

Conflicts:
	debian/control