Add some hardcoded autoconf configs in addition to the file-based system

As the title says (the branch is poorly named), autoconfig will now also consult an internal array of autoconfig strings (see input/autoconf_builtin.c) in addition to looking for files. This avoids relying on external files and needing to set a default for joypad_autoconfig_file and include various files. So far only 360 pads and the Thrustmaster 3-in-1 are included.

Further:
* Added function config_file_new_from_string to enable the above
* The input_player[n]_joypad_index options are now among the options saved on exit (if that option is on)