Adding an 'id' field to the 'Toggle Graphing of Maximum Reward' button

[canselcik]

I am in the process of developing an Android application for Eligius miners to monitor their account, and I will be using PhantomJS to capture the graphs and display them in the app. I wanted to toggle the graph view but since the button doesn't have an id, it is error-prone. Adding an id attribute should fix this.