DATAMONGO-899 - Ensure proper creation of index structures for nested entities.

Index creation did not consider the properties path when creating the index. This lead to broken index creation when nesting entities that might require index structures.

Off now index creation traverses the entities property path for all top level entities (namely those holding the @Document annotation) and creates the index using the full property path.

This is a breaking change as having an entity to carry the @Document annotation has not been required by now.

Original Pull Request: #168
DATAMONGO-899 - Polished API of new index creation abstractions.

Removed the introduction of the IndexDefinition being collection aware again. The collection an index is created in is now held in the IndexDefinitionHolder. This is mostly due to the fact that the IndexDefinition implementations can be used with MongoTemplate and the index opoerations take a collection alongside the index definition.

Made the IndexResolver API package protected so that we can further change it going forward. We should think about deprecating the collectionName attributes on index annotations as it doesn't make too much sense to manually configure the collection name for the indexes as the collection is predefined through the domain type setting here. This would allow us to remove the entire collection handling code inside the IndexResolver implementation.

Turned IndexDefinitionHolder into a value object.

Original pull request: #168.
DATAMONGO-909 - Compound index on inherited class should be created correctly.

With the overhaul of the index creation done in DATAMONGO-899 the CompoundIndex annotation is not longer just looked up at the concrete type but rather all its interfaces and super classes. So we just added an additional test to verify this behaviour.
DATAMONGO-827 - Allow index creation use mongodb auto generated names.

We now support letting MongoDB generate index names by introducing the attribute "useGeneratedName" to the @Indexed, @GeoSpatialIndex, @CompoundIndex annotations.