fix(AuthToken): Namespace observable methods

This prevents methods that use the regular methods internally from
clashing

server/boot/authentication.js

@@ -138,7 +138,7 @@ module.exports = function enableAuthentication(app) {
                 }
               );
             }
-            return authToken.validate()
+            return authToken.validate$()
               .map(isValid => {
                 if (!isValid) {
                   throw wrapHandledError(
@@ -153,7 +153,7 @@ module.exports = function enableAuthentication(app) {
                     }
                   );
                 }
-                return authToken.destroy();
+                return authToken.destroy$();
               })
               .map(() => user);
           });

server/models/auth-token.js

@@ -5,10 +5,10 @@ export default function(AuthToken) {
     AuthToken.findOne$ = Observable.fromNodeCallback(
       AuthToken.findOne.bind(AuthToken)
     );
-    AuthToken.prototype.validate = Observable.fromNodeCallback(
+    AuthToken.prototype.validate$ = Observable.fromNodeCallback(
       AuthToken.prototype.validate
     );
-    AuthToken.prototype.destroy = Observable.fromNodeCallback(
+    AuthToken.prototype.destroy$ = Observable.fromNodeCallback(
       AuthToken.prototype.destroy
     );
   });