Changes index rules to store index provider description

o Introduces SchemaIndexProviderMap in Kernel, TxState, IndexingService
  that verifies that provider and index rule match
o Adds SchmeaIndexProvider.Descriptor(providerKey, providerVersion)
o Changes IndexRules to store this descriptor
o Adds some BatchInserter tests
o Implements batch insert findNodesByLabelAndProperty
Merge pull request #678 from boggle/named-index-providers

Ensures that the same schema index provider used to create an index is used to access it