Add Userstyles feature for iOS

### Prerequisites

Please answer the following questions for yourself before submitting an issue. **YOU MAY DELETE THE PREREQUISITES SECTION.**

- [x] I am running the latest version
- [x] I checked the documentation and found no answer
- [x] I checked to make sure that this issue has not already been filed

### Problem Description

On iOS, there is no solution for Safari that completely supports user styles.

### Proposed Solution

Add native support for installing userstyles. There is support in https://github.com/quoid/userscripts, but it is very limited and does not support most standards: https://github.com/quoid/userscripts/issues/711

### Alternatives Considered

### Additional Information