Added tests for websafe_decode & websafe_encode
Added tests for websafe_decode & websafe_encode

These tests check conformity to the behaviour discussed during review of https://github.com/Yubico/python-u2flib-server/commit/49930e539deeede13fcc512feaf88bc414080a46

moreati/python-u2flib-server,Yubico/python-u2flib-server