Fix issues with multiple classes

[SandroHc]

Fixes all locations where multiple classes were not working as expected. Example that was failing before:

<table></table>
<script>
    new DataTable("table", {
        classes: {
            container: "my-container second-class",
        }
    })
</script>

This should be my last change for a while. Your support throughout these past days has been greatly appreciated!

[johanneswilm]

Looks good! Could you also add a note that the class name combinations need to be unique and it's not possible to use an empty string as the class names are used for the internal workings of sdt.

[SandroHc]

Done! Just finishing up the merge conflicts now.

[SandroHc]

Merge conflicts fixed