Add option to lock display builder to *.bob files

[kasemir]

By default, display builder runtime will open *.opi file unless there is also a *.bob file.
That's great for sites that use the display builder where most of the existing *.opi files work just fine.

Sites that want to run both BOY and display builder at the same time prefer to only open *.opi in the BOY runtime, so they need to disable the display builder falling back to *.opi files.

From within Display Builder runtime in Eclipse, need to invoke BOY runtime, ideally by finding it in Eclipse registry without adding explicit BOY dependency. From within Phoebus, call command line tool which can be configure to basically invoke "css -openFiles ..."