JobInstance-Metamodel for parameters based on blaze-domain

[beikov]

I prototyped #3 and now also a Job Metamodel with blaze-domain for a project and this seems worth including that into the blaze-job project as submodule.

The idea is to introspect the JobInstance entities with the declarative module of blaze-domain. This allows a user to annotate i.e. @DomainAttribute on some properties. The resulting metamodel can be used to create a CRUD UI for job instances. The only pitfal here is, that by default, a blaze-domain builder has no types registered. We'd need to create basic types as needed for any property that is discovered. A user can then decide with the metamodel if the type is supported.