Move contextual information to ASTContext
Overhaul formatting of properties

- Use shorthand notations `x.Member = ...` for getters.
- Go to new line on `with set` parts of setters in order to ensure
correct indentation
- No longer use `with get()` on getter-only properties

Fix #149
Fix https://github.com/fsprojects/VisualFSharpPowerTools/issues/345
Fix https://github.com/fsprojects/VisualFSharpPowerTools/issues/367