ModelDefinition: include `name` in the json file

Fix `ModelDefinition.getConfigData` to include model name in the
generated data.
Workspace: implement `listAvailableConnectors`

The list is maintained in the file `available-connectors.json` for now.
ModelProperty: implement `availableTypes`

A list of types to offer when creating a new property.
ModelAccessControl: improve metadata providers

Rename the property `humanized` to `name`.

Add `ModelAccessControl.getBuiltinRoles`.

Add the `cb` argument where missing.
Fix serialization of Model ACLs.

Add a new `embedded` property `name` that overrides the serialized
property name (`acls` instead of `accessControls`).

Fix deserialization of embedded arrays:
 - use `id` from the data as an id property - this has to be fixed
   later.
 - fill `relatedModel[foreignKey]` with the model name to preserve
   entity relation
connector: fix race condition in loadFromFile

Move calls of `loader.emit` to the very last callback, to make sure
the events are raised only once and only after all work has already
been done.
ModelAccessControl: rename 'method' to 'property'

Fix ModelAccessControl model to match the ACL definition expected by
loopback.