Use new Dependency#prerelease? method

[Resolver] Sort dependencies by number of possibilities, improving performance exponentially on large Podfiles

Fixes #2723.

Updates for https://github.com/CocoaPods/Core/pull/131.

Currently supported printer types are:
* `filename.html`: GraphHtmlPrinter
* `filename.txt`: GraphPrinter

For more printers see
https://github.com/ruby-prof/ruby-prof/blob/master/README.rdoc#printers.

Previously the header pattern was basically doing: `*.{.h}`, which has a dot too much,
but just happened to work because we don't actually use `Dir.glob` but implement our
own, which apparently isn't 100% similar.

Refactorings in Preparation to Framework Support

Thanks to @fabiopelosin.

Fixed wrong documented types drive-by.

This should make it more intuitive why we have to navigate there.

Instead of re-implementing the same call chain

This reverts commit 52b465c9.

This reverts commit 554e1951.

Conflicts:
	CHANGELOG.md

Fixes #2651