Improve no devices found text

[mpvader]

Below screenshot shows what you see after dragging in a node for which there is no matching device on the system. Lots of people will see it; for many it will even be the first thing they see; at least it was like that for me :).

Change the text to No matching devices found. Pick a different node from the palette., or something better.

[pkronstrom]

It might be better to show disabled dropdowns and a message below them instead of a big scary yellow box. Also, specifying the device type in the message is less ambiguous.

Here's a suggestion:

On a new node, the dropdowns are disabled and a red warning text.

When a previously selected device appears disconnected, the selected values are shown, but not editable. A different warning text is shown.

Proposed changes here

[pkronstrom]

New style

[pkronstrom]

Merged to master