Add boolean member to Perceptron to allow model initialization.
This is useful to show that the perceptron converges to different
solutions depending on initial values of w and bias.
Perceptron graphical example.
For the same data, the solution is different depending on initial values
of w and bias
Merge pull request #1007 from iglesias/feature/custom_init_perceptron

Add small functionality to perceptron and graphical example