Connection diagnostics

Display is toggled by clicking on the signal delay field in the Time Wrap display.
Connection is cached internally, and the last cached route is checked for quality.

Limitation: because no RT2 information is retained between scene changes, diagnostics
are only available for the active vessel, and only if the connection goes down while
the vessel is active.
Persistent diagnostics

Connection information is cached in a SignalRoutes object, which
loads and saves from the persistent.sfs and quicksave.sfs files.
Merge pull request #4 from bk2w/feature/persistent-diags

Feature/persistent diags