Extensively rewrite and clean up hammer

 - Support for building AppImages/AppBundles with "release_ember" command
 - Relocate all support scripts to "support" directory
 - Cleanups to enhance ease of understanding and maintainability
 - All build artifacts actually end up in the "work" directory now
 - All existing functionality maintained fairly transparently
 - Move all variables likely to be modifed (e.g. library version numbers)
   to start of hammer.sh script