dvcapture: change "no signal" message

[libbyhopfauf]

Once a device is detected, the playback window currently says "no signal" which is confusing for some users. I propose we change that message to one of these options (depending on how much detail/instruction we want to provide):

• "Device Connected"
• "Device connected. Please use the buttons below to control the deck."
• "Device connected. Please use the deck control buttons below for playback and capture." (could add "review" or "repack" in there too to acknowledge FF/REW)

One additional idea: If it's possible to detect if a tape is inserted or not, we could have the message say "Device Connected. Please insert a tape." if no tape is currently in the device. And then it could switch to one of the messages above.

[dericed]

@g-maxime, I think this was feasible in sony9pin, but with the dv control protocol, can we sense if the deck is in local/remote mode? and if there is a tape loaded?

[dericed]

done in #911