Map editor has now working context menu

Its natural to expect if there is Copy Paste option for CTRL+C CTRL+V keybindings to work accordingly

Currently they are not implemented

I suggest we make keybindings work for main functionality:

CTRL+C for Copy

CTRL+V for Paste

CTRL+SHIFT+V for Paste without external links (analogy for Paste without formatting in Windows)

CTRL+X for Remove