allow optgroups to be passed in as an array
added optgroup example
add optgroup_columns plugin and example
set searchField in optgroup example
reposition or close dropdown when adding item
specify order of optgroups
Merge commit '06083990003505e7640caf7ccf9b62102b2d882e' into optgroups
Added "equalizeWidth" and "equalizeHeight" options to "optgroup_columns" plugin (#8).
Minor consistency updates.