Client: Default dapimap to empty object

Without this, we have a BC break.

* src/client/Client.js (_init): Default program.dapimap to DataApiMediator
  instance to an empty object to maintain BC.

src/client/Client.js

@@ -347,7 +347,7 @@ module.exports = Class( 'Client' )
         this._factory.createDataApiMediator(
             this.ui,
             this._dataValidator,
-            this.program.dapimap,
+            this.program.dapimap || {},
             () => this.getQuote()
         ).monitor( this._dapiManager );