ui/ux: fix loading screen

- delays the loading screen image positioning to prevent incorrect
  placement due to variable times on screen rescaling
- removes the app suspension signal response which can't be
  differentiated from app termination
- removes lodepng which was used for vcards

Change-Id: I4cd46a9bdca40ef95fde89bd98e3b9f12bd8304b
Tuleap: #790