AUT-3779: Introduce locale section for mobile-specific pages

The decision to replay the Web journey within mobile apps could
present a maintainability challenge for developers. My sense is that
a clear way to identify the channel for content will help future
developers, and will be much easier than mixing Web and Mobile
content.

With this in mind, this commit introduces a new top-level property
to translation files called 'mobileAppPages' that is intended to hold
all content for pages that are specific to mobile.

The new block has been populated with content for all changes under
AUT-3779.

src/locales/cy/translation.json

@@ -165,6 +165,22 @@
       }
     }
   },
+  "mobileAppPages": {
+    "signIn": {
+      "title": "Mewngofnodi i GOV.UK One Login",
+      "header": "Mewngofnodi i GOV.UK One Login",
+      "paragraph": "Gallwch ddefnyddio eich GOV.UK One Login i brofi eich hunaniaeth a chael mynediad at rai o wasanaethau’r llywodraeth.",
+      "button": "Mewngofnodi"
+    },
+    "accountNotFound": {
+      "title": "Nid oes gennych GOV.UK One Login",
+      "header": "Nid oes gennych GOV.UK One Login",
+      "paragraph1": "Nid oes GOV.UK One Login ar gyfer ",
+      "paragraph2": "Mae angen i chi fewngofnodi gyda chyfeiriad e-bost sydd â GOV.UK One Login i brofi eich hunaniaeth.",
+      "tryAnotherLinkText": "Rhowch gynnig ar gyfeiriad e-bost arall",
+      "findOutMoreLinkText": "Darganfyddwch fwy am ddefnyddio GOV.UK One Login"
+    }
+  },
   "pages": {
     "signInOrCreate": {
       "mandatory": {

src/locales/en/translation.json

@@ -165,6 +165,22 @@
       }
     }
   },
+  "mobileAppPages": {
+    "signIn": {
+      "title": "Sign in to GOV.UK One Login",
+      "header": "Sign in to GOV.UK One Login",
+      "paragraph": "You can use your GOV.UK One Login to prove your identity and access some government services.",
+      "button": "Sign in"
+    },
+    "accountNotFound": {
+      "title": "You do not have a GOV.UK One Login",
+      "header": "You do not have a GOV.UK One Login",
+      "paragraph1": "There is no GOV.UK One Login for ",
+      "paragraph2": "You need to sign in with an email address that has a GOV.UK One Login to prove your identity.",
+      "tryAnotherLinkText": "Try another email address",
+      "findOutMoreLinkText": "Find out more about using GOV.UK One Login"
+    }
+  },
   "pages": {
     "signInOrCreate": {
       "mandatory": {