feat: add back button and i18n support on 404 page (#1700)

src/assets/translations/en-US.json

@@ -2,6 +2,7 @@
   "APP_NAME": "Mifos X",
   "Logged in as": "Logged in as",
   "Remember me": "Remember me",
+  "not_found_subtitle": "Oops.. Looks like this page doesn't exist.",
   "languages": {
     "en-US": "English",
     "fr-FR": "French",

src/assets/translations/es-MX.json

@@ -2,6 +2,7 @@
   "APP_NAME": "Mifos X",
   "Logged in as": "Sesión activa como",
   "Remember me": "Recordarme",
+  "not_found_subtitle": "Vaya... Parece que esta página no existe.",
   "languages": {
     "en-US": "Inglés",
     "fr-FR": "Francés",

src/assets/translations/fr-FR.json

@@ -2,6 +2,7 @@
   "APP_NAME": "Mifos X",
   "Logged in as": "Logged in as",
   "Remember me": "Remember me",
+  "not_found_subtitle": "Oups.. Il semble que cette page n'existe pas.",
   "languages": {
     "en-US": "English",
     "fr-FR": "French",