[vi mode] add option to make yanking copy text to system clipboard

[laur89]

If user

1. selects text in visual mode
2. presses y key (for yank)

then yanked text is not available in system clipboard.

I propose adding an option to Settings -> editor -> 'Vi Input mode' menu to toggle this behavior.

Running vnote 3.15.1

[tamlok]

"+y

[laur89]

Personally never used it with vim due to it being a handful to type.

If this option would not be considered, I'll close the ticket.

[tamlok]

Will support key mapping to this as something like <space>y in the future.