Bug 1445798 - Add Leanplum settings opt-out strings needed for bug #1454686; r=mcomella

To allow users to opt-out from receiving LeanPlum messages we need a new setting added.
This are the Strings for the title and summary of that setting.

Localization notes also added as this Strings will ship before the feature.

Decided to suppress all UnusedResources Lint errors for android strings until the patch for #1454686 lands as using in-line suppression caused other errors.
Ran Lint locally, the build passed.

MozReview-Commit-ID: 9Kx567ruY3n
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--HG--
extra : rebase_source : acb555719b4da9199364ca737ff140012dacb47c

mobile/android/app/lint.xml

@@ -241,6 +241,9 @@
              preprocessed_resources res/raw folder. Lint reports it as unused. We should get
              rid of the file eventually. See bug 1268948. -->
         <ignore path="**/raw/.mkdir.done" />
+        <!-- Needed to ignore currently unused resources added as per bug 1445798
+             Suppression to be removed when the along with the ptch for bug 1454686 -->
+        <ignore path="**/res/values/strings.xml" />
     </issue>
     <issue id="Usability" severity="error" />
     <issue id="UseCheckPermission" severity="error" />

mobile/android/base/strings.xml.in

@@ -225,7 +225,6 @@
   <string name="pref_whats_new_notification">&pref_whats_new_notification;</string>
   <string name="pref_whats_new_notification_summary">&pref_whats_new_notification_summary;</string>
 
-
   <string name="pref_feature_tips_notification">&pref_feature_tips_notification;</string>
   <string name="pref_feature_tips_notification_summary">&pref_feature_tips_notification_summary;</string>