Currently, if you press DELETE the entire sprite is removed.
If you have a selection and press delete, everything is lost.
This commit checks if you have a selection. If so, it only removes the selected area.
Im trying to solve issue https://github.com/nesbox/TIC-80/issues/455.
When copying a hex palette from the web, it palette may contain spaces, tabs or carriage commands (\r or \n).
Pasting it on TIC-80 will not work, making the users life difficult (they have to fix the string in an editor).
This commit enables pasting hex palettes with blank spaces.
Guilherme Medeiros