[Settings] Improve separator line logic throughout settings screens

[SylvesterWilmott]

Currently, app settings separator lines don't follow any logic. To create a more readable and understandable UI, this should be amended using the following logic:

• All sections are followed by a separator line
• Any settings not in a section are followed by a separator line

Screens this applies to:

• Site settings
• Notification settings
• App settings

Example:

[stale]

This issue has been marked as stale because:

• It has been inactive for the past year.
• It isn't in a project or a milestone.
• It hasn’t been labeled [Pri] Blocker, [Pri] High, or good first issue.

Please comment with an update if you believe this issue is still valid or if it can be closed. This issue will also be reviewed for validity and priority (cc @designsimply).