Add links to new single pom sample project

A number of our users don't have sufficient experience with Maven to write their own pom.xml file from scratch, and the examples (multi-module maven project) is too complex.
Thus I've added this: https://github.com/deeplearning4j/dl4j-examples/tree/master/standalone-sample-project.
https://github.com/deeplearning4j/dl4j-examples/pull/668

Docs should be updated where appropriate to point users to that.

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