Escape stop tx only

[dl1jbe]

A discussed in Issue #344 this PR add the following features:

• New keyword 'ESC_STOP_TX_ONLY' modifies ESCAPE key behavior, so that it only stops an ongoing CW or voice message. The gradual wipe off of information from exchange and call input field are blocked.
• Add two new keys to wipe out (and restore afterward) the actual field the cursor is in - Ctrl-W - or the whole information line - Ctrl-U.

[N0NB]

I ran from this branch during last weekend's ARRL 160m 'test. It worked as expected so I think you can merge this, Tom.

[dl1jbe]

Thanks or the test Nate. Will merge it in now.
At the moment I am experimenting to get the UNDO feature also used if you still use ESCAPE to wipe out the input fields stepwise.