Fix #191 & Fix #193

Added showIcon option (set to true by default). While set to true, all
icons for their associated selected options are shown in the button.
When false, no icons are shown in the button. Added setStyle function,
which allows classes to be added/removed from the button and its
container.
Merge pull request #196 from caseyjhol/master

Fix #191, #193, and add new setStyle function for more flexibility