Added possibility to let others sidr opened when opening a new one

[wtfred]

Add "closeOthers" property to choose if others menu should be closed on one sidr opening

[wtfred]

property "closeOthers", default "true" to keep the actual behaviour.
Setting it to "false" will make the others sidr panel to stay open when opening one

(sorry for my bad english...)

example:

$('#update-menu-trigger').sidr({
    side: 'right',
    displace: false,
    closeOthers: false
});