Versioning stack artifacts

PRODUCING ARTIFACTS

Update starter

1. put tag in pom.xml 
2. commit
3. tag with mentioned tag, push tag

Update image (doesn't incorporate automated test yet)

1. Update content
2. Update devfile version, increment Dockerfile version in devfile
3. Commit devfile referencing next tag
4. build image with latest,  major.minor, major.minor.micro

Update devfile

1. Increment version in devfile
2. Send PR to https://github.com/odo-devfiles/registry/
3. At this point it can be used unofficially as:
    * odo registry update DefaultDevfileRegistry https://github.com/scottkurz/registry
    4. Tag repo with devfile number 

If this ends up being too loose, we could modify this so that we only check in x.y.z-rc1 into our own repo, and then have the PR to the official odo registry use x.y.z

CONSUMING ARTIFACTS

1. Devfile - git checkout devfile-<x.y.z> (devfile version)
2. Image - git checkout image-<x.y.z> (openliberty/application-stack image version)
3. Default Starter - `git checkout default-x.y.z (in https://github.com/OpenLiberty/application-stack-starters)