Allow setting cursor color with escape sequence again.

This commit 97feb543 broke support for changing cursor color
by escape sequence if value starts with `CursorShape=`.

printf '\e]50;CursorShape=0;CustomCursorColor=#ff5f00\a'

This also implements support for setting cursor color and also for cursor
blinking without changing the current profile what is purpose of the
97feb543 change.

(cherry picked from commit 7a9d8839)