[SNAP-1067] Optimizations seen in perf analysis related to SnappyData…

… PR#381 (#11)

 - added hashCode/equals to UnsafeMapData and optimized hashing/equals for Decimal
   (assuming scale is same for both as in the calls from Spark layer)
 - optimizations to UTF8String: cached "isAscii" and "hash"
 - more efficient ByteArrayMethods.arrayEquals (~3ns vs ~9ns for 15 byte array)
 - reverting aggregate attribute changes (nullability optimization) from Spark layer and instead take care of it on the SnappyData layer; also reverted other changes in HashAggregateExec made earlier for AQP and nullability
 - copy spark-version-info in generateSources target for IDEA
 - updating snappy-spark version after the merge

Conflicts:
	build.gradle
	sql/core/src/main/scala/org/apache/spark/sql/execution/aggregate/HashAggregateExec.scala

sql/core/src/main/scala/org/apache/spark/sql/execution/aggregate/HashAggregateExec.scala

@@ -323,7 +323,7 @@ case class HashAggregateExec(
   private val bufferSchema = StructType.fromAttributes(aggregateBufferAttributesForGroup)
 
   // The name for Fast HashMap
-  private var fastHashMapTerm: String = _
+b  private var fastHashMapTerm: String = _
   private var isFastHashMapEnabled: Boolean = false
 
   // whether a vectorized hashmap is used instead