Mountmaster Achievement (Additions to taldin's PR)

Same as #4200 with added info on the stats page
This is just Mountmaster, right? Not Triad Bingo as well?

On Friday, December 12, 2014, Blade Barringer <notifications@github.com>
wrote:

> In CHANGELOG.md
> <https://github.com/HabitRPG/habitrpg/pull/4374#discussion-diff-21761236>:
>
> > @@ -1,282 +0,0 @@
> > -<a name="">My app - Changelog</a>
>
> Is it cool with everyone that the changelog is being deleted?
>
> —
> Reply to this email directly or view it on GitHub
> <https://github.com/HabitRPG/habitrpg/pull/4374/files#r21761236>.
>