Passed a new variable 'preview' to the render function

This variable determines whether we are viewing the custom certificate for a particular user, or if we are simply previewing it. This may be needed for some elements. For example, an element may retrieve the data for when the custom certificate was issued, but if the user has just set up the custom certificate and no issue has been created then this data is missing, so in this case we pass that the user is previewing the custom certificate so other data can be shown.