[WIP] Custom Scrollbars

Another pass at integrating custom scrollbars, properly.

**Notes:**
* The custom scrollbars are **blue** while in development, do help differentiate between native and custom
* The new editor (still WIP) uses a textarea, which is not compatible with any form us browser-compatible  custom scrollbars, so that uses the default still.
* The code needs so much cleaning.

**Todo:**
- [ ] Reset the scrollbar (to get the correct size) when:
    - [ ] Infinte scroll has happened
    - [ ] A view has changed (new post)
- [ ] Figure out why the scrollbar doesn't show on the editor preview
- [ ] Clean up code
- [ ] Test in ***all*** the places