Add self generating models

* Add PeriodicFunction, SineWave, TriangleWave, SquareWave classes
* Added random periodic chooser to the front page
Adds functions

* add periodic, square, sine, triange and random generators
* using ActiveModel::Model and ActiveModel::Conversion
* looking to instagram
Add handling of widget as a partial

* add partial render endpoint without layout
* add instagram widget