accompanies reorganization of mounts page, in PR #3906

Accompanies the pull request at [https://github.com/HabitRPG/habitrpg/pull/3906](https://github.com/HabitRPG/habitrpg/pull/3906)

I updated the mounts page to be organized the same way as the pets page, and so accordingly I added mounts in a couple of files in habitrpg-shared. I consider this pull request and the one at habitrpg to be part of the same contribution because they go together, but for the sake of having my UUID handy on both posts, I'll include it here too.

Thank you~! <3

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