Changes the data store bound to this LoadMask.
@param {Ext.data.Store} store The store to bind to this LoadMask
function(store, initial) {
        var me = this;
        me.mixins.bindable.bindStore.apply(me, arguments);
        store = me.store;
        if (store && store.isLoading()) {
            me.onBeforeLoad();
        }
    }