Automate asstes building in pkgbuild
- Add yarn-offline-cache distfile so that yarn build can be done during port build
- Add TARGET make-yarn-cache to build the yarn-cache-offline distfile
- Compile ruby assets during port build
- Remove multiple ${MV} statements for renaming *.example files *.sample files
- Use TMPPLIST to generate the pkg-plist dynamically instead of a huge static pkg-plist