Settings: Overhaul the Security page

This improves the organization of this page, which is starting to become
a bit of a mess. The "Hide images and video events" option is moved
here, and the page is rebranded accordingly for "Security & Safety".
Unnecessary headings are removed, and the ignored users button is moved
to the top of the page.

Explanations for the import/keys buttons are added. The key display
is removed as it's not useful for the user (because they don't know what
to do with it) nor developers (because you can't copy it.) We can add
it back somewhere else.

This has the added benefit of making the whole page fit in the default
settings window size too.

src/settings/NeoChatSettingsView.qml

@@ -48,7 +48,7 @@ KirigamiSettings.ConfigurationView {
         },
         KirigamiSettings.ConfigurationModule {
             moduleId: "security"
-            text: i18n("Security")
+            text: i18nc("@title", "Security & Safety")
             icon.name: "preferences-security"
             page: () => Qt.createComponent("org.kde.neochat.settings", "NeoChatSecurityPage")
             initialProperties: () => {