Integrate code formatting

This fixes #287.

It includes:
 - Format document and format selection
 - Read configuration from `TextStylePolicy` and `FSharpFormattingPolicy` inside Xamarin Studio
 - Add `FSharpFormattingPanelWidget` to change formatting options

Caveats:
 - Doesn't save documents after formatting (C# formatter has similar behaviours)
 - Doesn't highlight selection after formatting (C# formatter has similar behaviours).

We could force saving documents using `IdeApp.Workbench.ActiveDocument.Save()` if it makes more sense.

Please consider this as a baseline version.
I don't have more time to work on this now. If anyone would like to improve this, please do.