Merge pull request #1000 from sjwarner-bp/isogram-starter-impl

Isogram: add starter implementation

exercises/isogram/src/main/java/IsogramChecker.java

+class IsogramChecker {
+
+    boolean isIsogram(String phrase) {
+        throw new UnsupportedOperationException("Delete this statement and write your own implementation.");
+    }
+
+}