Removing unused initialize function

This was left over from some boilerplate
Setting the duration programatically

Determine the duration based on the data in the model. We add an
arbitrary Mya figure for the last period since it has no "end"
Use the get() method to find the attribute
Add the era duration to the model

This allows us to use it after rendering for interaction with the mouse.
Add right boundaries and an interval to the model

This creates a pixel boundary for each era. This makes the style and
behavior style in sync in the mousemove functions below.