activate sanitizer, sub and sup

opengraph_parser is basically unmainted, issues are ignored
or deliberately closed without fixing. It pollutes the global
namespace and has no verification of correctness.

The opengraph gem has basically the same issues, not really maintained,
unreleased patches on master since over a year, not really smart either.

So I created my own version and while at it, why not strive try to be
complete and robust, although it's still a work in progress.

This also improves general URL detection by parsing them
from the message after stripping markdown.

An additional dependency was added to support
fetching sites that require cookies to work at all.
For the same reason Faraday's default redirect limit was
bumped.

Spring is the recommended application preloader for rails

In order to use the system Fedora/EPEL ruby we need to install
minitest in production. See comments in Gemfile.

From upstream changelog,

    Deprecate delay extension for ActionMailer 4.2+ . [seuros, #1933]
    Poll interval tuning now accounts for dead processes [epchris, #1984]
    Add non-production environment to Web UI page titles [JacobEvelyn, #2004]

Debian already have 3.2.6 and I'd like to keep both versions in sync.