Load OData Core annotation vocabularies implicitly in MetadataParser

Now that MetadataParser understands how to parse the "annotation" fragments, it will be useful to load the "core" vocabularies from the OData specification either automatically or provide simple option to load automatically.

For example, the TripPin service's $metadata uses these standard annotations in its data model, however the vocabularies are not defined anywhere in "References", they are inherently assumed to be available. Olingo framework should also provide same capabilities in the "server-core-ext" module.