Added "jQuery UI" style method access; Added `get_toolbar_element` method

- Added "jQuery UI" style method access:
    The toolbar object instance is associated to the element using
    `$.data()`, and calling `$.toolbar("method", arg1, arg2, ...)` is
    equivalent to calling `toolbarObj.method(arg1, arg2, ...)`. Also,
    method names starting with an underscore ("_") are ignored.
- Added a `get_toolbar_element` method:
    This method simply allows retrieving the tool buttons container.
    Usefull to set the selected state of the buttons from outside the
    plugin.
Changed method name from `get_toolbar_element` to `getToolbarElement`

- Changed method name to follow current naming style.
- Also added documentation about the new method.
Update minified version
Conflict around the way the toolbar arrow is referenced