Change default print margin from 100 to 80 per style guidelines

[DartBot]

This issue was originally filed by @chrisbu

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What steps will reproduce the problem?

Tools > Preferences > Show Print Margin = 100

Style guidelines on dartlang says "AVOID lines longer than 80 characters" - the editor should help to enforce this

What version of the product are you using? On what operating system?

Dart Editor 0.1.0.201110311319 Build 970

[stevemessick]

I'll handle this one.

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Set owner to @stevemessick.
Added Accepted label.

[devoncarew]

We should consider removing the text field to adjust the value for the print margin - just turn it into a boolean to toggle the (80 char) margin on and off.

[floitschG]

The style-guide is non-binding (and the 80 chars in the guide is just an "AVOID").
So I don't think we should restrict the editor to 80 chars only (especially as I don't see a high maintenance cost in keeping the option).

[stevemessick]

Both good points. For the moment, I'm just changing the default from 100 to 80. Once the formatter is released, I think it makes sense to take another look at this preference to see how best to present the print margin and the formatter line length preferences in as simple a way as possible.

[stevemessick]

Added Fixed label.