added number constraints to ports

app/src/main/res/xml/account_editor_xmpp.xml

@@ -60,6 +60,7 @@
         android:key="@string/account_port_key"
         android:title="@string/account_port"
         android:singleLine="true"
+        android:inputType="number"
         android:dependency="@string/account_custom_key"
         />
     <EditTextPreference
@@ -102,6 +103,7 @@
     <EditTextPreference
         android:key="@string/account_proxy_port_key"
         android:title="@string/account_proxy_port"
+        android:inputType="number"
         android:singleLine="true"
         />
     <EditTextPreference