Only assign application identifier when we're running an app with system trust scope

Signed-off-by: Simon Busch <morphis@gravedo.de>
Drop old plugin implementation

Signed-off-by: Simon Busch <morphis@gravedo.de>
Drop old apps not used anymore from headless-allowed list

Signed-off-by: Simon Busch <morphis@gravedo.de>
Print out database quota requirements from applications

Until we have decided how to implement this we just print out the requirement and allow a
quote of 5 MB.

Signed-off-by: Simon Busch <morphis@gravedo.de>