DATAMONGO-1025 - Fix creation of nested named index.

We new prefix explicitly named indexes on nested types (eg. for embedded properties) with the path pointing to the property. This avoids errors having equally named index definitions on different paths pointing to the same type within one collection.

Along the way we harmonized index naming for geospatial index definitions where only the properties field name was taken into account where it should have been the full property path.

Original pull request: #219.