Revert "Don't show buttons after last tab, if Tab Mix Plus configured to "New tab button: on Right side""
Not needed anymore, see https://bitbucket.org/onemen/tabmixplus/commits/b91167ef36ce144aa6d6ece232c859b0a14452c2
(related to #96)
This reverts commit d2bede729545cfbe80299f2c5f2cb08bb8d52870.