Absorbed the gui db-viewer into gcylc.

 * converts "cylc dbviewer" into a suite chooser dialog for gcylc, and removes the former. 
 * gcylc can switch between registered suites, and 
 * can be started without specifying a particular suite
 * GUI right-click db operations (unregister, copy, etc.) still available by right-click in the new suite chooser dialog (perhaps not very intuitive...).
 * took "start-up views" preference to gcylc.rc (was a gcylc command line option)
 * updated all documentation
 * "File -> Register New Suite" writes a rudimentary suite.rc template if the chosen suite does not exist already.