[ZEPPELIN-922] New interpreter registration mechanism for Scalding

### What is this PR for?
Applies the new interpreter registration mechanism to Alluxio interpreter.

### What type of PR is it?
Improvement

### Todos
- [x] Remove static registration in org.apache.zeppelin.scalding.ScaldingInterpreter
- [x] Create interpreter-setting.json

### What is the Jira issue?
[ZEPPELIN-922](https://issues.apache.org/jira/browse/ZEPPELIN-922)

### Questions:
* Does the licenses files need update? No
* Is there breaking changes for older versions? No
* Does this needs documentation? No

Author: Igor Drozdov <[email protected]>

Closes apache#1759 from DrIgor/ZEPPELIN-922 and squashes the following commits:

921fe1c [Igor Drozdov] New interpreter registration mechanism for Scalding

scalding/src/main/java/org/apache/zeppelin/scalding/ScaldingInterpreter.java

@@ -57,18 +57,6 @@ public class ScaldingInterpreter extends Interpreter {
   public static final List NO_COMPLETION =
     Collections.unmodifiableList(new ArrayList<>());
 
-  static {
-    Interpreter.register(
-      "scalding",
-      "scalding",
-      ScaldingInterpreter.class.getName(),
-      new InterpreterPropertyBuilder()
-        .add(ARGS_STRING, ARGS_STRING_DEFAULT, "Arguments for scalding REPL")
-        .add(MAX_OPEN_INSTANCES, MAX_OPEN_INSTANCES_DEFAULT,
-                "Maximum number of open interpreter instances")
-        .build());
-  }
-
   static int numOpenInstances = 0;
   private ScaldingILoop interpreter;
   private ByteArrayOutputStream out;

scalding/src/main/resources/interpreter-setting.json

@@ -0,0 +1,19 @@
+[
+  {
+    "group": "scalding",
+    "name": "scalding",
+    "className": "org.apache.zeppelin.scalding.ScaldingInterpreter",
+    "properties": {
+      "args.string": {
+        "envName": null,
+        "defaultValue": "--local --repl",
+        "description": "Arguments for scalding REPL"
+      },
+      "max.open.instances": {
+        "envName": null,
+        "defaultValue": "50",
+        "description": "Maximum number of open interpreter instances"
+      }
+    }
+  }
+]