WCAG: prevent click-ability for unread-message counter, add description to image button

Signed-off-by: Andy Scherzinger <info@andy-scherzinger.de>

app/src/main/res/layout/rv_item_conversation_with_last_message.xml

@@ -92,6 +92,7 @@
                 android:layout_height="18dp"
                 android:layout_alignParentEnd="true"
                 android:layout_marginStart="8dp"
+                android:clickable="false"
                 android:gravity="top"
                 android:lines="1"
                 android:textAppearance="@style/ChipUnreadMessagesTextAppearance"

app/src/main/res/layout/search_layout.xml

@@ -95,6 +95,7 @@
                     android:layout_width="48dp"
                     android:layout_height="48dp"
                     android:layout_gravity="center"
+                    android:contentDescription="@string/nc_settings"
                     android:scaleType="fitCenter"
                     android:transitionName="userAvatar.transitionTag"
                     app:cornerRadius="@dimen/button_corner_radius"