Added core changes and docs required for simm valuation demo.

core/src/main/kotlin/com/r3corda/core/math/Utils.kt

@@ -0,0 +1,7 @@
+package com.r3corda.core.math
+
+import java.math.BigDecimal
+
+fun Iterable<BigDecimal>.sum(): BigDecimal {
+    return this.fold(BigDecimal.valueOf(0)) { a: BigDecimal, b: BigDecimal -> a + b }
+}

core/src/test/kotlin/com/r3corda/core/math/Utils.kt

@@ -0,0 +1,14 @@
+package com.r3corda.core.math
+
+import org.junit.Test
+
+import org.junit.Assert.*
+import java.math.BigDecimal
+
+class Utils {
+    @Test
+    fun sum() {
+        val calculated = listOf(BigDecimal.valueOf(1.0), BigDecimal.valueOf(5.0)).sum()
+        assert(calculated == BigDecimal.valueOf(6.0))
+    }
+}