header (C) fixes
Main/USB/linux: fix some doxygen
Main/USB/linux: move USBProxyLinuxChooseMethod to USBGetDevices
Main/linux/USB: unit tests for the code changed in r71554 and r71557
Main/linux/USB: better permissions checking and code cleanup
Main/linux/USB and RDP/client/vrdp: clean up the handling of the USB device tree path and get rid of data duplication
Main/USB/linux: minor fixes to USBGetDevides
Main/USBProxyServiceLinux: split out USB enumeration from USBProxyServiceLinux.cpp and HostHardwareLinux.cpp into a separate file