Improve settings import

### Prerequisites

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

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

### Problem Description

The user cannot select specifically which settings should be imported.

### Proposed Solution
Add an option to choose what should be imported from the settings file.
Additionally, there should be a "Success" dialog.

Example:


### Additional Information

The source issue can be found [here](https://github.com/AdguardTeam/AdGuardForSafari/issues/563).

Also, validation is worth considering.