The designs for the call details show information on the type of the call:
https://gitlab.gnome.org/Teams/Design/app-mockups/blob/master/calls/calls.png
So f.e. "Cellular", "Matrix WebRTC Video Call".
These properties can potentially also be useful in choosing the mechanism to
use for the audio controls from the call display.
This "ui-active" property should be set to FALSE for new incoming calls and set
to TRUE after a short delay of 20ms. This property is used to delay showing the
call display and starting to ring.
This delay gives DBus clients like
phosh-antispam (https://gitlab.com/kop316/phosh-antispam)
some time to make a decision whether a call should be hung up or not and defer
starting to ring and showing the display only afterwards.
We need a proxy object because implementing the CuiCall interface in the
CallsCall base class has it's own set of problems (f.e. the "state" property
would have a type collision CallsCallState vs CuiCallState).
