Change graph aspect ratio

This adds the ability to resize graphs according to pre-defined aspect ratios. Currently the following are supported:

- 16:9
- 16:10
- 2.40:1
- 4:3 (the default)

Additionally, dirty checking has also been added for global config values. If the aspect ratio or column number is changed, the user is prompted before they leave the page if they haven't saved.

I chose the aspect ratios pretty arbitrarily... they were just the ones that came to mind. let me know if you want more/less/different ones.

Let me know what you think