Support equally sized bars in bar chart

[benmccann]

I would like an option to have equally sized bars.

I think this option should be on by default. The bars on the bar chart right now may be of different widths. This is very unusual behavior for a bar chart. I'm not aware of a use case that motivates the current behavior

Discussion on Slack: https://chartjs.slack.com/messages/C0N98KP1N/p1500887069899049