sdk: Refactor AbstractObjectProvider

[moritzsommer]

Previously, the AbstractObjectProvider only worked with Identifiables, which made it incompatible with the new version of the AAS metamodel.

This renames and restructures both the AbstractObjectProvider and the AbstractObjectStore. In all non-abstract subclasses where Object appears in the class or method name, it has been replaced with Identifiable. Old classes are still available with a deprecation warning. The refactoring includes:

1. DictObjectStore -> DictIdentifiableStore
2. SetObjectStore -> SetIdentifiableStore
3. LocalFileObjectStore -> LocalFileIdentifiableStore
4. CouchDBObjectStore -> CouchDBIdentifiableStore

Moreover, AbstractObjectProvider and AbstractObjectStore are now generic to be able to handle more classes than just Identifiables.

In order to handle the new AASDescriptor, a new class HasIdentifier has been added. It is intended to be an abstract superclass for all classes that have an identifier, but are not Identifiables.

The docs, comments and variable names have been adapted accordingly.

Fixes #428

[s-heppner]

I'm fine with the current design, except for the small nitpicks I have in the comments.

I also agree that the newly created methods and classes should be used everywhere in our code.
However: We absolutely need the old methods retained wrapping the new methods with a deprecation warning, otherwise we need to release this as a version 3.0.0, which I don't think we should.

This applies to the methods from:

• DictObjectStore
• SetObjectStore
• LocalFileObjectStore
• ...

and all other methods that have been refactored.

[s-heppner]

LGTM. Is this ready to be merged now?

Btw, it looks like your Linter is configured to a shorter line length than defined (historically) in our project. We demand a maximum 120 characters per line, as per our CI (therefore, shorter is fine as well.)

[moritzsommer]

Btw, it looks like your Linter is configured to a shorter line length than defined (historically) in our project. We demand a maximum 120 characters per line, as per our CI (therefore, shorter is fine as well.)

My local linter is also set to a line length of 120 characters. However, I never split words or other structural elements of the documentation, e.g. :class:`AbstractObjectProviders <.AbstractObjectProvider> must remain in one line. If this exceeds the character limit of the current line, it must be pasted onto the next line, which might create a big blank space in the current line. Do you handle it differently? Or where does it look like I am using the wrong settings?