Refactor classes that are only useful for GModel source models

[planger]

Move base diagram module and operation handlers that operate directly on GModels (as a model source) to the dedicated package org.eclipse.glsp.server.gmodel and add prefix GModel in the class name.

[tortmayr]

Thanks @planger. Changes look mostly good to me, I only have a few inline comments.

One additional discussion point:

Due to our current naming scheme the handler names tend to become relatively
long (especially implementation specific handlers for the emf/direct gmodel usecases).
I'm wondering whether we should shorten this a little bit by dropping the Action/Operation part. At the moment action and operation names are unique anyways so appending this information adds no additional value.
e.g. GModelApplyLabelEditOperationHandler => GModelApplyLabelEditHandler.
@planger WDYT?

[tortmayr]

We should decide whether we want to import Inject from google.inject or javax.inject and double-check all imports to ensure consistency

[planger]

In most places we use google.inject. So I used this one now consistently.

[tortmayr]

With the LayoutOperationHandler being generic and reusable for all implementations shouldn't it be bound as part of the parent module?

Same is probably true for the CutOperationHandler

[planger]

in fact, LayoutOperationHandler was already bound in the superclass anyway. But I now also pushed the cut operation handler up into the super class (and removed both from the subclass).

[planger]

Due to our current naming scheme the handler names tend to become relatively
long (especially implementation specific handlers for the emf/direct gmodel usecases).
I'm wondering whether we should shorten this a little bit by dropping the Action/Operation part. At the moment action and operation names are unique anyways so appending this information adds no additional value.
e.g. GModelApplyLabelEditOperationHandler => GModelApplyLabelEditHandler.
@planger WDYT?

Thanks for the review! I've addressed all inline comments. Regarding the class name... I'm not so sure. They tend to get long, that's true, but this way they are also more explicit and I don't think it is a problem. But I'd be also fine renaming them and omit the Operation in their name. I didn't do it yet, so if you'd like this to be done, let me know.

[tortmayr]

Thanks for the fast update. LGTM!