Misc UI improvements

[mshedsilegx]

Some minor suggestions for UI improvements (comes from feedback of our users):
1- The mouse over message for QR code is blank. I suggest to show: QR Code for secret URL
2- The possibility of a custom mouse over message for button: [Create the Secret] and/or a field in the OTS homepage where it is possible to include an HTML formatted custom message. Above or below the create secret dialog box
3- Make the How does this work message a popup window, so it can be viewed, then closed, without losing what is currently being done

Thanks again for a fantastic product !