[Jaxrs-spec] Update jaxrs-spec to interface/impl pattern #4509

[jfiala]

PR checklist

• [x] Read the contribution guildelines.
• [x] Ran the shell/batch script under ./bin/ to update Petstore sample so that CIs can verify the change. (For instance, only need to run ./bin/{LANG}-petstore.sh and ./bin/security/{LANG}-petstore.sh if updating the {LANG} (e.g. php, ruby, python, etc) code generator or {LANG} client's mustache templates)
• [x] Filed the PR against the correct branch: master for non-breaking changes and 2.3.0 branch for breaking (non-backward compatible) changes.

Description of the PR

see #4509 This was originally filed against master of 2.2.2-SNAPSHOT with PR #4717, but then scheduled for release 2.3.0.

I split interface/implementation and cleaned up the implementation so it doesn't have annotations. I also fixed the generatedAnnotation.mustache to contain the check for {{^hideGenerationTimestamp}}. The samples were completely outdated (old package names etc.), I updated them to the current state.

Open issues (from master):

• There are errors in the FakeApi.java/FakeApiServiceImpl.java due to joda and @PATCH, which I left as is, these have probably been fixed in the master.
• CodegenResponse.java is missing the vendorExtensions, so I added a TODO marker at AbstractJavaJAXRSServerCodegen.java.