editors/mp: Update to 5.31
- LICENSE was changed from GPLv2 to a Public Domain license
- UI options have been reconfigured so that if the user installs a GUI (GTK2, GTK3, or QT5), mp-5 is also usable in the console via the NCURSES or ANSI options
- mpsl and supporting data are no longer installed, but rather compiled into the mp-5 binary
- Add pkg-message to explain the GUI color scheme change and how to revert to the previous color scheme if so desired