Add support for localized enyo signals

Enyo signals are always global and affect all instances of all apps (on the same page). This PR allows signals to be localized to one specific app. This is useful when multiple independent apps or instances are present in the same document. In an additional PR I'll try to implement a global switch to make all signals local by default, but I haven't figured out how, yet.

Enyo-DCO-1.1-Signed-off-by: Johann Jacobsohn j.jacobsohn@satzmedia.de