Ask for explicit confirmation before deleting a wiki in the WikiManager

When deleting a wiki, the current user action is to:

• go to the wiki manager via "Home > Wiki index"
• click on the "delete" icon
• on the upcoming confirmation page, confirm by pressing "yes"

As deleting a wiki (unlike most other actions) has no undo, this should be made a bit harder.

a) mention in the confirmation page that this action can not be undone
b) add an input field on the confirmation age where the user has to type in the name of the wiki to be deleted. If submitting that form with "yes", if the name does not match, the wiki is not deleted, but the confirmation page is shown again with an error message.