* allow modules to still use libpng12-dev but show a message for them to be updated
* change libpng-dev dependency to libpng12-dev for Jessie and older
* use opengl for x11 targets
* disable stark engine on opengles builds (currently doesn't build) - #1834
* no longer any need for SDL_CONFIG=sdl2-config
* rp_module_menus is no more - instead use rp_module_section with one of
- core (core packages)
- main (main packages - which will be installed by default in the image)
- opt (optional packages)
- exp (experimental packages)
- driver (driver packages)
- config (configuration packages / tools)
* The setup menu organises the data based on the above sections. more could be added in the future if needed. Packages (internally modules), can be added / configured / removed individually, or as entire sections.
* The setup menu will automatically detect if a binary is available to be installed. the nobin flag is no longer needed. modules that install directly from binary via aptInstall or via a prebuilt binary need to use an install_bin_ function instead of install_
* rp_module_section of type "config" will have the "gui_" function called first if it's available, otherwise a standard depends/sources/build/install/configure will be called
* configure is no longer used for "gui" configuration function - use gui_ instead. Had already started to move to this before, but now it is required.
