job file: send error from namerslv to /dev/null

Stop output of "/etc/resolv.conf does not exist".
Visualization settings override cylc-graph.
Merge pull request #546 from matthewrmshin/namerslv

job file: send error from namerslv to /dev/null
Tidier grouping logic.
Merge pull request #544 from arjclark/cylc-graph-fix-visualisation

cylc graph: use visualization settings
Removed old CLI switch reference.
Merge pull request #550 from arjclark/doc-tidy

removed old cylc gui CLI switch reference