Activate SNI

[Bramzor]

Might be a good idea to add the activation of SNI to the manual.
http://directadmin.com/features.php?id=1100

Caused me some time to figure that out.

[Wouter0100]

Development of this plugin is suspended because of native Let's Encrypt support in DirectAdmin since version 1.49.2.

If this features isn't being released or very limited, we'll continue development.