186 show increment controls histogram

[coyle5280]

This closes #186

Context

This PR modifies histogram.js and histogram.jst.ejs. Two methods were added to histogram.js to handle the increment and decrements of the input histogram fields along with the events to call those methods. Html was added to histogram.jst.ejs to display the increment and decrement buttons.

Acceptance

• [x] User clicks on the increment buttons and see the field value increase by one.
• [x] User clicks on the decrement button and see the field value decrease by one.
• [x] Changes using the increment or decrement buttons are reflected in the table and histogram.

[alissarose]

👍 looks great to me --> integration ready