i18n: Add Minerva specific message key for last modified bar

This is currently defined in MobileFrontend which uses it for
Special:MobileWatchlist.

We shouldn't use two messages for 2 purposes so let's give it
its own dedicated message.

Change-Id: Id5df6aad20815b88b8bd2685514e7eb3237a5b3b

i18n/en.json

@@ -3,6 +3,7 @@
 		"authors": []
 	},
 	"skinname-minervaneue": "MinervaNeue",
+	"minerva-last-modified-date": "Last edited on $1, at $2",
 	"minerva-talk-add-topic": "Add discussion",
 	"mobile-frontend-console-recruit": "\\o/ Hey! This is open source software and we need volunteers to help us build this thing, make it better and fix any bugs that you might be seeing in this JavaScript console!\n\nYou can find our backlog @ https://phabricator.wikimedia.org/project/profile/67/",
 	"mobile-frontend-cookies-required": "Cookies are required to switch view modes. Please enable them and try again.",

i18n/qqq.json

@@ -12,6 +12,7 @@
 		]
 	},
 	"skinname-minervaneue": "The skin name for MinervaNeue.",
+	"minerva-last-modified-date": "Text that displays the date the page was last modified. Parameters:\n* $1 - date\n* $2 - time\n{{Related|Mobile-frontend-last-modified}}",
 	"minerva-talk-add-topic": "Label for button which shows at bottom of talk pages in mobile view prompting addition of topic",
 	"mobile-frontend-console-recruit": "Message that is displayed in the JavaScript console aimed at developers in an attempt to recruit volunteers. The \\o/ emoticon is a man with his arms in the air with the purpose of drawing attention to the message. If this doesn't translate into the destination language feel free to omit it or use something more applicable.",
 	"mobile-frontend-cookies-required": "Error message shown when user attempts to switch site modes and cookies are not enabled.",

includes/skins/SkinMinerva.php

@@ -734,7 +734,7 @@ class SkinMinerva extends SkinTemplate implements ICustomizableSkin {
 			$lastModified = $this->msg( 'mobile-frontend-history' )->plain();
 		} else {
 			$lastModified = $this->msg(
-				'mobile-frontend-last-modified-date',
+				'minerva-last-modified-date',
 				$this->getLanguage()->userDate( $timestamp, $user ),
 				$this->getLanguage()->userTime( $timestamp, $user )
 			)->parse();