1. Added entities, entity defintions.
2. QSIM schema asserted per model/graph.

* [QSIM,EXT] The first use case now adds an entity to the quantity.
* [QSIM_BG,SC] Shorter code by using a new predicate from LIST_EXT.
* [QSIM_BUILD,NEW] Allow the addition of entities, entity defintions, and their relation to quantities.
* [QSIM_BUILD,SC] Relocated the predicates that create a new graph/model and a new resource (not used yet).
* [QSIM_BUILD,EXT] Assert the QSIM schema in each model/graph separately. This will allow for completely independent simultaneous simulations at some point.
* [QSIM_BUILD,EXT] Extended the QSIM schema for entities and entity defintions and their relations to quantities.
Integrating the SW into QSIM:
1. Relate a concept to a resource.
2. Export the external triples about the related concept.

* [QSIM_BUILD,NEW] Added predicate for relating a concept to an existing resource.
* [QSIM_MOD,EXT] Add concept-introduced triples to QSIM model export.