MOCCACAL-29: Selecting a color for the calendar should colorise the input

I tried some alternatives, but it seems the class="procolor" is really needed on the input element; otherwise some background-image styling takes precedence.
The only alternative is to add the CSS-class via JavaScript: `$('MoccaCalendar.MoccaCalendarClass_0_color').addClassName('procolor')` ... but I do not think that is better.
Btw, I see some ugly inline `<script>` that can be scrapped from the sheet, now. I hope this somewhat outweights the disadvantage of having to render the input-tag manually.