Additional HTML5 demo service changes

I pushed my initial demo service patch set in #73 a bit too prematurely. The HTML5 DOCTYPE breaks rendering of the map because the 100% height of the div not applied by virtue of its parent lacking a defined height. 

66bd5af79c7db5609b930b945287cbefb97160a7 fixes this by setting the height and width of the html and body elements to 100% too, and decreases the div size by 2 pixels for its border. The CSS calc() function is relatively new and only supported by recent browsers.

The other changes are just minor improvements to the generated HTML by using newlines and improving indenting.

I've not included an experimental patch with sets the Content-Security-Policy HTTP header for the demo service pages, because I'm unsure this is something MapCache should do. It should preserve the header if its set by the souce WMS for text/html GetFeatureInfo requests, but with no CSP header set no policy restrictions are applied. So it's unlikely to break functionality if MapCache doesn't pass along the header. If you're interested in this patch I can polish it up and send it in a separate pull request.