Generator-related cleanup - the second iteration

Implement `AclDefinition` model replacing `model.options.acls` object.

Move value providers from generator-loopback to loopback-workspace:

 - `Project.listAvailableConnectors(cb)` provides a list of connector modules to choose from
 - `PropertyDefinition.availableTypes` provides a list of types to choose from, e.g. `string` or `object`.
 - `AclDefinition` has three providers - `accessTypeValues`, `builtinRoleValues`, `permissionValues`.

Fix datasource configuration problem caused by recent migration to `app.boot`.

/to @ritch please review.