Fix handling of anonymous object types

In LoopBack, the method PersistedModel.updateAll describes the return type using an inline (anonymous) definition:

{
  returns: {
    arg: 'info',
    type: {
      count: {
        type: 'number',
        description: 'The number of instances updated',
      },
    },
    root: true,
  },
}

Before this change, remote invocation of updateAll was crashing the process with the following error:

AssertionError: type must be either an array or a string.

This patch fixes the problem as follows:

A try/catch block is introduced to correctly report any sync errors via the callback
The type registry was improved to recognize anonymous object types and use the "object" converter for them.

/cc @angfal @ewrayjohnson

Checklist

[x] New tests added or existing tests modified to cover all changes
[x] Code conforms with the style guide

strongloop / strong-remoting

Fix handling of anonymous object types #472

Related issues

Checklist