Clean problem-desc and styles . Fix fontSize, add noDefaultStyle

[vexorian]

• Now that there are no tags, I think it is best to prefix output with Returns: as we need to differentiate input and output and that's the way the arena does it.
• fontSize CSS needs to be in the main template for the option to work.
• Removed the color settings for the fancy example numbers from the themes.
• Now that the color themes are separate templates, I cleaned them up and added comments to encourage users to make their own.
• Added a noDefaultStyle option. The old customStyleSheet replaced the whole style sheet, but now customStyle doesn't . I think it is useful to allow users to add style, but I also need to make it possible to remove all style from HTML (I like to use an external CSS file I can modify) so this function disables all style inside the html.