[minor] Dialog title mismatch for Preferences/Settings

[lofidevops]

Steps to reproduce:

• Open Revolt in GNOME
• Click on application name to get action dropdown
• Select "Preferences"

What should happen:

• "Preferences" dialog opens

What happens instead:

• Action dropdown appears, lists "Preferences" (correct)
• Dialog opens (correct)
• Dialog title is "Settings" not "Preferences"

Notes:

Probably best to change dialog title to "Preferences", rather than change the dropdown item to "Settings":

• "Preferences" is the typical name in GNOME apps (as far as I know, let me know if I should look for HIG citation)
• helps distinguish Revolt "Preferences" from "Riot Settings"

[aperezdc]

@kwill Good catch!