Where is the gesture button?
When you are in the Gesture Settings you need to click on the tab that says "Dolphin Sonar Settings" in the bottom right hand corner.  There you'll have the option to "Enable bottom left button."  This puts the new "dual purpose" Gesture &amp; Sonar button in the bottom left hand corner.  

FWIW, I think the whole Sonar thing is annoying and I don't understand why they reduced the customization options.  I prefer my gesture button on the right!