Model - merge resource & map using anonymous submodels and field.isStorage

[mdutoo]

Merging resource & map field types has been thought about for a long time.

The right way to do it is

• by letting a resource field definition specify, alternatively to a model type as for now, a complete embedded model definition, which would be similar to a map field definition having also a @type.
• this new case would be triggered by field.isStorage=true (false being the backward-compatible default), see Model - field.isStorage to allow to index subresource fields #168. Therefore anonymous models would allow to easily enable (or disable) field indexing whatever the inherited model type by easily overriding field indexing configuration (queryLimit).

Conceptually, this would make field.isStorage similar to model.isStorage, and containing models being similar to point of views guiding the true nature of contained subresource models, up to a possible later even more configurable model router.