Fixes for yeoman generator

This patch contains changes required by `yo loopback` and fixes for bugs discovered along the way.

 - package: add mocha as dev-dep and test script
 - ModelDefinition: include `name` in the json file
 - Workspace: implement `listAvailableConnectors`
 - ModelProperty: implement `availableTypes`
 - ModelAccessControl: improve metadata providers
 - Fix serialization of Model ACLs.
 - connector: fix race condition in loadFromFile
 - ModelAccessControl: rename 'method' to 'property'
 - Fix deserialization of embedded key-value maps

/to @ritch please review