ENYO-2457: Added support for mozSystem and mozAnon on Firefox OS

ENYO-2457: Added support for mozSystem and mozAnon on Firefox OS

We can create xhr with the mozSystem and mozAnon features by passing booleans in the ajaxProperties such as:

var x = new enyo.Ajax({
    url: "http://query.yahooapis.com/v1/public/yql?format=json",
    mozSystem: true,
    mozAnon: true
});

I decided to use prefixed names for the properties because they are not standard. There is a check in the source code to make sure we're running on Firefox OS before trying to add this type of thing.

mozAnon and mozSystem do not depend on each other. You can use any of them without using the other.

Enyo-DCO-1.1-Signed-off-by: Andre Alves Garzia <andre@andregarzia.com>