Update the FAQ to Elm 0.19

[souserge]

I noticed that the FAQ section is saying that it's for Elm 0.19, but in reality, contains a lot of examples and sources from earlier versions of Elm. Thus, I decided to fix what I can and ask for a review for the people who are more knowledgable of Elm that I. Here's what I've updated:

• Elm tools' names (elm install instead of elm package install, elm make instead of elm-make etc.);
• links to point to latest packages (mostly elm/<some-package> instead of elm-lang/<some-package>);
• The section about handling navigation (the library was moved to Browser.Navigation in 0.19).

I would also like to ask someone to review sections:

• How can I recover when elm make fails with errors like "... openFile: does not exist"?;
  • How do I install an Elm package that has not been published to packages.elm-lang.org for use in my project?;
• The sections about native-modules;
• The section about ! [] construct.

As far as I understand, many things in these sections are either outdated or not relevant in Elm 0.19.

[fredcy]

I reverted those broken local page links and committed the rest of the PR as is. Thanks again.