Enables toggle behaviour like Bootstrap accordion

[julianalucena]

Hides selected panel when the user clicks on it again, like Bootstrap accordion behaviour (closes #3):

Also, I fixed a strange behaviour: accordion select function was called twice when the panel was clicked by the user. You can see this through the console:

[david-duncan]

I built on top of your PR in #5 and removed the click handler from the component itself and placed it as an action in the component. This prevents certain contents of the accordion panel from toggling the collapse of the accordion, and ensures the intended behavior of the accordion collapsing can only be toggled from inside of the accordion header.