Respond to lost connection better in gcylc suite views.

View-clearing code was called repeatedly instead of just once when not
connected to the suite. In the graph view this involves a graphviz
subprocess, repeated calls to which could result in hundreds of error
dialogs if the subprocess was failing for some reason.

Also tidies a bit of old code, splits the dot- and tree-view updater
classes into separate files like the graph-view updater, and renames a
couple of files more sensibly.
Fix gcylc

Following b1f7bc69c929b3507dabffd5aad8fdf04e74d7ab, `gcylc` with no
argument returns 'NoneType' object has no attribute 'printcfg'. This
fixes the problem.
Merge pull request #866 from matthewrmshin/fix-gcylc

Fix gcylc
Merge branch 'master' into gcylc-lost-connections
Merge pull request #865 from hjoliver/gcylc-lost-connections

Respond to lost connection better in gcylc suite views.
cylc/cylc#865: restore initial graph name.
Merge pull request #869 from benfitzpatrick/cylc-gui.graph-stopped-initial-name

#865: restore initial graph name.
Determine correctly if a task host == localhost
Merge pull request #873 from matthewrmshin/task-host-is-localhost

Correctly determine if a task host == localhost