add FAB content description

// FREEBIE

res/layout/conversation_list_fragment.xml

@@ -17,6 +17,8 @@
                   android:headerDividersEnabled="false"
                   android:footerDividersEnabled="false"
                   android:dividerHeight="1px"
+                  android:nextFocusDown="@+id/fab"
+                  android:nextFocusForward="@+id/fab"
                   tools:listitem="@layout/conversation_list_item_view"/>
 
     <com.melnykov.fab.FloatingActionButton
@@ -26,6 +28,8 @@
         android:layout_gravity="bottom|right"
         android:layout_margin="16dp"
         android:src="@drawable/ic_add_white_24dp"
+        android:focusable="true"
+        android:contentDescription="@string/conversation_list_fragment__fab_content_description"
         fab:fab_colorNormal="?fab_color"
         fab:fab_colorPressed="@color/textsecure_primary_dark"
         fab:fab_colorRipple="@color/textsecure_primary_dark" />

res/values/strings.xml

@@ -853,6 +853,9 @@
     <!-- conversation_list -->
     <string name="conversation_list__menu_search">Search</string>
 
+    <!-- conversation_list_fragment -->
+    <string name="conversation_list_fragment__fab_content_description">New conversation</string>
+
     <!-- conversation_secure_verified -->
     <string name="conversation_secure_verified__menu_security">Security</string>
     <string name="conversation_secure_verified__menu_verify_identity">Verify identity</string>