Updated Greek Translations (#3741)

Hello,

we have updated the core Greek translation and added Greek translation
to Alerts module.

Thank you!

---------

Co-authored-by: Savvas Adamtziloglou <savvas-gr@greeklug.gr>
Co-authored-by: Konstantinos <geraki@gmail.com>
Co-authored-by: Veeck <github@veeck.de>

modules/default/alert/translations/el.json

@@ -0,0 +1,4 @@
+{
+	"sysTitle": "MagicMirror² Ειδοποίηση",
+	"welcome": "Καλώς ήρθατε, η εκκίνηση ήταν επιτυχής!"
+}