v3.1: usbview 3.1 release

version 3.1
- remove now-unnecessary policykit/pkexec support
- appstream metadata added
- gtk+ dark theme fixes
- gtk+ tooltip fixes

usbview 3.0

No longer requires root access, nor access to the debugfs USB devices file. Relies on sysfs only now.

usbview 2.1

v2.1

usbview v2.1 release