Use objectpath more generically to fix requirejs issues

It looks like the ObjectPath dependency was breaking angular-schema-form installs in environments that use require.js (see https://github.com/mike-marcacci/objectpath/issues/1), because ObjectPath couldn't automatically register itself with angular. I've removed the auto-registration in a new version of ObjectPath, and this PR fixes the issue accordingly.

I don't use either AMD or require.js in my schema-form projects, so maybe @frhd or @skchrko can check this out?

Please note that this requires users to upgrade ObjectPath to 1.1 when they upgrade ASF (assuming they aren't using bower).