Add help links and descriptions to analyzers

* I'm not an english native speaker so I hope that I didn't type anything that doesn't make sense.
* I placed the code to generate the URL for help links in a separate file so it's easy to change.
* Some analyzers like `TernaryOperatorAnalyzer` have 2 diagnostics with different IDs, maybe they should point to the same help page
* Obviously none of the page exists right now. A potential solution could be to return null inside the help link generating class for now and switch to the final URL once enough documentation is written.

> For some of them I didn't had any good description that
> wasn't a repetition of the text so I avoided to add it
> but still added the help link to all of them.
> 
> While reviewing all of them I also added the tag to get
> greyed-text on analyzer indicating unnecesary constructs:
> 
>     customTags: WellKnownDiagnosticTags.Unnecessary
> 
> Follow the discussion in #78