[apparmor] Let's enable AppArmor by default (why not?)

[Ben Caradoc-Davies]

On 18/11/17 04:27, intrigeri wrote:
> Thanks in advance, and sorry for any inconvenience it may cause (e.g.
> the AppArmor policy for Thunderbird has various issues in sid; all of
> those I'm aware of are fixed in experimental already).

Where "various issues" means no thunderbird external helpers work under 
xfce. Not a single one, as far as I can tell. And there goes another 
one: what happened to my .signature? I have filed as many bugs as I can 
given the time available. I will file one more for the missing 
.signature, and then I am disabling apparmor.