Refactor resource tab implementation to be generic for all entity types and explicitly support de.systopia.eck

[jensschuppe]

Resolves #9.

[jensschuppe]

@bjendres I added a redirect in the resource create form when there already is a resource for the entity. This, along with the changes in 3a2bcaa6e5e05516d8a1e7d4f5d0cee2a3437975, will make the resource tab work for any tabset that uses Core's templates/CRM/common/TabHeader.js, as does the ECK extension.

However, the tab label element does not update (except for the count badge), i.e. it will not become de-greyed and the ? icon will remain. Do you think it should be merged without resolving that?

[jensschuppe]

Added some changes regarding:

• suggesting resource label - now tries to retrieve the entity label from the BAO's label field, if one exists
• retrieving and creating resources using BAO methods instead of APIv3
• redirecting after creating a resource

I also rebased everything onto the current master.

This is now ready for some extended testing.