tox: Fix g_strdup() error

We must dup the empty string as well because we free priv->name in
neuland_tox_finalize().
window: Fix source indentation
window: Fix issues when accepting requests

When a request has been accepted, it now disappears from the contact's
list (which only shows requests when the "show-requests" action's state
is TRUE). Also, once no requests are left, automatically change the
action's state to FALSE, so that the new and old contacts show up
again.