sr/cli/gtk/qt: Fix package version numbers / docs.

The next (and first) libsigrok release will be called 0.1.0.

The next (and first) libsigrokdecode release will be called 0.1.0.

The next sigrok-cli release will be called 0.3.0 (as we already had a 0.1
and 0.2 release of sigrok-cli; those did not yet use the libs, though).

sigrok-gtk and sigrok-qt didn't have any releases yet, so their version
numbers are set to 0.1.0.

Also, consistently use three numbers/digits for our version numbers.