Add panelHeaderTemplate and panelFooterTemplate properties to MultiSelect

[mertsincan]

Templates of the panel header and footer.

panelHeaderTemplate(options) {
    // options.className: Style class of the panel header.
    // options.checkboxElement: Default checkbox element created by the component.
    // options.checked: Whether the all checkbox is checked.
    // options.onChange: Change event of toggleable checkbox.
    // options.filterElement: Default filter element created by the component.
    // options.closeElement: Default close element created by the component.
    // options.closeElementClassName: Style class of the close container
    // options.closeIconClassName: Style class of the close icon
    // options.onCloseClick: Click event for the close icon.
    // options.element: Default element created by the component.
    // options.props: component props.
}

panelFooterTemplate(options) {
    // options.props: component props.
}