Packr 4.0.0 mutiple launchers (executables) per application

1. Added an option to specify the JRE directory in the configuration file.
2. Changed the default config file name from config.json to <app name>.json
   where app name is the value of the --executable field passed to packr-all.jar.
   If the executable name is myapp (or myapp.exe on Windows) then the default config file name will be myapp.json instead
   of config.json.
   • Creating multiple launchers requires running packr multiple times or creating a config JSON via alternative means and copying and renaming the launcher to match the config name.
3. Please update your Maven and Gradle build scripts to point to https://artifactory.nimblygames.com/artifactory/ng-public.
   • Gradle will soon require HTTPS and the -snapshot and -release repository URLs are for publishing, not downloading.