better neuron design, remove method alias for activate, propagate on activation
add input & output layers + tests
better neuron, settings, input_layer, add propagation for neuron & layer, fix neuron tests
Merge branch 'develop'

* develop:
  better neuron, settings, input_layer, add propagation for neuron & layer, fix neuron tests
  add input & output layers + tests
  better neuron design, remove method alias for activate, propagate on activation