Change color of cursor according to mode

[fvacek]

Mode indicator color is changed according to mode used. I thing that also cursor color and possibly also cursor line color can vary to inform user about current mode without looking to bottom left corner.

[the-mikedavis]

You can theme cursors by mode with the ui.cursor.{normal,insert,select} theme keys and the primary cursor with ui.cursor.primary.{normal,insert,select}: https://docs.helix-editor.com/master/themes.html#interface