Fix NSFW property on User model and add missing properties (#256)

<!-- If this pull request closes an issue, please mention the issue
number below -->
Closes #193 

## 💸 TL;DR

This pull request addresses two issues on the `User` model:
* NSFW property is returning the wrong value - it currently returns the
"I am over 18 and want to see NSFW content" property, rather than the "I
am NSFW" property.
* Two underlying properties available on the Data API (isMod and isGold)
are not available on the User model. I am now exposing these properly,
using the current "Reddit Premium" terminology instead of Reddit Gold.

## 🧪 Testing Steps / Validation
I have tested these locally by modifying files in the node_modules
folder. However it is not possible for me to run full CI on this.

For some time I have had my own User model that transforms these values
in the same way.

## ✅ Checks
<!-- Make sure your pr passes the CI checks and do check the following
fields as needed - -->
- [ ] CI tests (if present) are passing
- [X] Adheres to code style for repo
- [X] Contributor License Agreement (CLA) completed if not a Reddit
employee