Allow the user to customise the click query

Hi !

   To be able to integrate jQuery-Collapse on one of my project, I had to customise the element we can click on to collapse a section.

    This patch let you define a new option __clickQuery__ to select an element in the "Summary" header. To be able to select a specific button instead of the entire header fox example.

Hope this will help

Thank you

Aurélien