Sidr: add new source type

Not sure if this will be valuable to you or not, but here is some changes.

When source type is Array, Sidr will wrap each array element in div and
add defined CSS classes. Example:

$().sidr({
source: [{
className: "sidr-header",
source: "header.header"
}, {
className: "sidr-menu",
source: "ul.menu"
}]
});

This option allows to apply custom CSS styling to matched set of elements.