Refactored the code.

I have added fixtures to the test case, so now It don't have repeated
code.
Created first test for NeuralLayer class.

This test will describe the behavior of a NeuralLayer.
Refactored code.

The name Neural has been corrected to neuron. It implies that
Neural.java has been renamed to Neuron.java too.
Refactored code.

The name of the test has been changed from NeuralTest to NeuronTest
because it has been changed Neuron class before.
Refactored the code

NeuralLayer and NeuralLayerTest has been renamed to NeuronLayer and
NeuronLayerTest respectively.

Also NeuronLayer has a default new constructor.
Added addNeurons method

This method accepts an undefined number of neurons and add they
to the layer
Added comments to addNeurons method
Revised tests

- Added to all test the mark @Test.
- Completed the setUp method
Refactored Neural to Neuron
Created test for getNeurons
Validated getNeurons method
Added a test for addNeurons
Overloaded addNeurons method

Now you can add a collection of neurons too.
Added a verification to the overleaded addNeurons method
Added equals test.
Added equals method
Added a new check to equals test

Now it check if two layers without neurons are equals too.
Refactored equals method.

Now distinguish correctly between two layers.
Refactored code.

Changed layerEmpty_ to emptyLayer_
Added removeNeuron method