Make builder configurable

[duncdrum]

Enable node only builds via gulp, give users the option to specify gulp or ant as builder.

Add another prompt to have the ant generate -dev.xar on demand.

see #11 #61 #113

[duncdrum]

Ok here is the target project layout for pure gulp builds. Next step implementing that layout inside the index.js file and making the generated gulpfile flexible with respect to hybrid builder apps with optional ant and with respect to the special need to deploying library packages (when using pure gulp builds).

├── .dockerignore
├── .git
├── .github
│   └── workflows
│       └── exist.yml
├── .gitignore
├── .npmignore
├── Dockerfile
├── Readme.md
├── dist
│   ├── package.xar
│   └── xar
│       └── …
├── package-lock.json
├── package.json
├── src
│   └── … 
└── test

basically lots of moving stuff around. Old root contents -> src, except Dockerfile, package.json, .exist…