Effortless multiple nodes selection alternative

Description

Give an alternative to select multiple nodes without the need of the keyboard.
Simplify the process of activating the selection marquee as an alternative to the shift + click and drag, which is sometime cumbersome in some occasion.

Justification

Quality of life request, for lazy guys like me.

Implementation Details

Double click in empty canvas to activate the selection marquee.
We can then now select multiple nodes without to have to shift click from the keyboard.


Thanks @facelessmindz for your feature request!