Unit tests for Grovers, Measure nodes

[ttoktassynov]

Purpose

Add unit tests for Grovers, measure nodes, write a test util function to validate flow output

Changes

• Fixed issue In node-red-node-test-helper input handler not called on errors and warnings #83 and now can test invalid input on Grovers' node in dcd0a5c
• Added generic test util function to validate output of the flow based on the given input
• Added a test case for Measure Node that checks if correct output is received in the end
• Fixed Quantum Circuit to have a reference to shell instance, so that we could stop by referencing inputNode's shell instance later in the unit tests. Last three changes here 2dad31a
• Refactored grovers_spec.js to use testUtil function correctOutputReceived to validate output 89d17fc
• Changed the error condition testing so that error handling in the nodes are consistent, meaning that they still call done(err) in node constructor. Changes are in 535c054

New Requirements

• Quantum Circuit Node has to store in its instance a reference to shell instance
• Every error handling shouldn't call done(err), but rather call this.error(err.message) and return afterwards. This is because test helper will be able to test such conditions.