Add parser for netlify.toml

[calavera]

- Do you want to request a feature or report a bug?

This is a new feature.

- What is the current behavior?

There is no way to test and verify the contents of a netlify.toml file

netlify.toml files should be tested in a new view, much like the redirects view, but with their own parser. We should also add a link in the header to arrive to the view, a link in the home screen and a direct link to the documentation.

[andreasvirkus]

I'd love to pick this up, although I'm not familiar with Elm... but there's always a first! For parsing TOML, should I go with something like https://package.elm-lang.org/packages/zwilias/elm-toml/latest/?

Edit: how does Netlify parse the config file - does it ignore invalid blocks? Should the parser initially only focus on the headers spec of the config file or should it cover more things?