added propper open/close event triggering to panels and sub-panels (side-panels still not done)...

Signed-off-by: Alex A. Naanou <alex.nanou@gmail.com>
started testing the panel constructors + found a bug: open/close events get triggered on panel drag/sort...

Signed-off-by: Alex A. Naanou <alex.nanou@gmail.com>
updated todo + minor changes...

Signed-off-by: Alex A. Naanou <alex.nanou@gmail.com>