Triple opt-in should be optional and get a description text

[arnekolja]

With e6ff178 sort of a triple opt-in got implemented to avoid the issue of some email clients automatically opening links without user interaction.

Imho this should be optional, so I suggest to do the following:

• Add a TS setting for it.
• Either add doApprove as a link parameter when this setting is set, or enhance the if statement in the controller with a check for it.

Also, the link is displayed without any description. That's unfortunate, so there should also be a descriptive text in the frontend output.