Add the ability to pass through the BatchScanner/BatchWriter
configuration options to Cosmos via Store, #3

Created getters/setters for a BatchWriterConfig member to "tweak" writes and a
readThreads member that controls the maximum number of threads Cosmos
will use with a BatchScanner.
Merge branch 'master' into accumulo-1.4

Conflicts:
	core/src/main/java/cosmos/impl/CosmosImpl.java
	core/src/main/java/cosmos/store/PersistedStores.java