Reordering project file

[jindraivanek]

This allows us to use Mechanic on project file.

• when calling CLI with one argument, it is expected to be .fsproj, and it will be overwritten with new order
• SymbolGraph.solveOrder works with generic type with selector for filename
• In project handling, XmlNode of items is saved, and then used for reordering
• SymbolGraph.solveOrder support files other than .fs, its treated as file without dependencies

There seems to be a problem with island nodes (files without dependencies) in ordering, I fix that in separate PR.

This don't support msbuild properties mentioned in #61 and #62.

[forki]

hugs!!!

[jindraivanek]

Thanks :)