RO 3.5.4

- RO.Prefs.PrefWdg: Added a contextual menu with Help (if helpURL provided) to all controls; formerly only the status bar had this.
- RO.Comm.HTTPGet: deregister tcl callbacks before cleaning up the connection (this seems cleaner, though it works either way).
- Switched to git and updated releaseNewVersion.py and documentation accordingly.