Added event as parameter to on_close function, fixes #15
Now possible to erase cell in sheet table on right click, hopefully a valid commit this time... Closes #3
Removed event.preventDefault from on_close, because its  redundant.. Should fix #15
#3 Moved the setters for prev and current into on_sheet_mouse_down due to that on_sheet_disable_context_menu is called later in some browsers and OS
Merge pull request #22 from OlofFredriksson/master

Fixes for #15 and #3