move strings to resource file

res/values/strings.xml

@@ -406,4 +406,7 @@
     <string name="manage_space_description">Settings, database and server certificates from %1$s\'s data will be deleted permanentlty. \n\nDownloaded files will be kept untouched.\n\nThis process can take some time.</string>
     <string name="manage_space_clear_data">Clear data</string>
     <string name="manage_space_error">Some files could not be deleted.</string>
+
+    <string name="permission_storage_access">Write access is required to upload/download files.</string>
+
 </resources>

src/com/owncloud/android/ui/activity/FileDisplayActivity.java

@@ -220,9 +220,9 @@ public class FileDisplayActivity extends HookActivity
                 // code is still in place in case this changes in the future
 
                 // Show explanation to the user and then request permission
-                Snackbar.make(findViewById(R.id.ListLayout), "Write access is required to upload/download files.",
+                Snackbar.make(findViewById(R.id.ListLayout), R.string.permission_storage_access,
                         Snackbar.LENGTH_INDEFINITE)
-                        .setAction("OK", new View.OnClickListener() {
+                        .setAction(R.string.common_ok, new View.OnClickListener() {
                             @Override
                             public void onClick(View v) {
                                 requestWriteExternalStoreagePermission();