Update support documentation for modern times

Summary:
Basically similar to D13941 but a little more extreme:

• Really strongly emphasize reproducibility for bug reports, and set users up for rejection if they don't satisfy this.
• Really strongly emphasize problem descriptions for feature requests, and set users up for rejection.
• Get rid of various "please give us feedback"; we get plenty of feedback these days.
• Some modernization tweaks.
• Split the support document into:
  • Stuff we actually support for free (security / good bug reports / feature requests).
  • Stuff you can pay us for (hosting / consulting / prioritization).
  • A nebulous "community" section, with appropriate (low) expectations that better reflects reality.

My overall goals here are:

• Set expectations better, so users don't show up in IRC expecting it to be a "great place to get amazing support" or whatever the docs said in 2011.
• Possibly move the needle slightly on bug reports / feature request quality, maybe.

Test Plan: Read changes carefully.

Reviewers: chad

Reviewed By: chad

Differential Revision: https://secure.phabricator.com/D14305