Prepare digikam to be able to open a camera gui on a given Solid Device UDI.

- move code to open a usb device and a gphoto2 camera by UDI to separate methods
- add a method that accepts a UDI and determines which of the two above methods to call
- move code to check and create a label for gphoto2 cameras to separate methods
- use queued signals instead of single shot timers to call methods from command line paramters