Modified login on api & client and unlike_mix, like_mix, fav_track, unfav_track commands on client.

Login command on api was modified to allow user to log in with different credentials even
if currently logged in. Subsequent changes were made on client.

unlike_mix, like_mix, fav_track, unfav_track were modified to check if user was logged in and
to do so, get_logged was added to client.

And other various fixes.