"Finish" button logic should be part of the core wizard

You can implement a Finish button today as shown by
basic-finishbutton.html example but you have to write logic on top of
the core wizard. This is a core scenario so let's move logic inside.
"Finish" button should also affect state of "Last" not just "Next"

Note: 'hidden' CSS class used is present only in Bootstrap 3
update docs and examples with new Finish button
Finish button logic should also hide Back button
Merge pull request #97 from stefann42/master

 "Finish" button logic should be part of core wizard logic