Better hlint integration

[NobbZ]

Currently the hlint integration works as follows:

• Mark a linted occurence with a special background color
• Provide an Alt+Enter thingy that allows to ignore this kind of linting
• On hovering you get a little tooltip that shows hlints message but unformatted which is hard to read if the lint is getting more complex

I'd suggest following:

• Mark background as before
• Provide Alt+Enter thingy that allows to ignore this kind of lints as before
• Provide some window which collects all lints throughout that file and shows them formatted and readable
• Provide some extension to the Alt+Enter thingy that allows you to replace the current "wrong" expression with the suggested one of hlint
• Remove that useless tooltip

[carymrobbins]

I agree with everything except -

Remove that useless tooltip

Possibly the formatting could be improved, but I think having an annotation popup is pretty useful.

In fact, that's the standard way to show warnings/errors in the source.