delete on selected text deletes ports

[tanismar]

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On yarpmanager++, when opening a new external port, text gets selected in porder to write the corresponding source/destionation address. If using backspace to remove text, everything is fine, but if 'delete' is used, it deletes the port instead of the text. This should be modified so that if the text is selected, only text is removed.

Also, a mouse button to enable to pan around by click and drag (middle button for example), would be very useful too.