Merge pull request #49 from jocelynlih/paul

Full set of assets for indoor environment
Just renaming our level template to the inside template. Will create a new one for the other environments
Our art pipeline is now part of the build. No longer need to run update_art manually. In addition, the artgen script has been updated to act like a makefile of sorts, only updating art assets that have actually changed. (see issue #42)
Art assets should be placed into their appropriate location in the Art/Staging/* tree. If the asset is complex and is built from a master (for example, a high-resolution or vector asset) then that master should live in the Art/Master tree. See comments here: https://github.com/jocelynlih/SwiftGameBook/commit/2cf29c69fbaae6a2f85a875c83ae824d511d6243