WebServer: switch to HTML5 and add normalize.css trimmed down to our needs.

Notes:

* seekbarchleft and seekbarchright width in player.html is set via js
* only controls.html isn't valid HTML5
* switch to Arial font
Use font-size:0 for #seekbar td.

This fixes a visible white line showing below the seekbar.
Use pre for the debug section.
web/info.html: document where the mpchc_np id is used.
Update controls.html.

* use lowercase method "post"
* make the reloadenabled checkbox centered
* move inline style to default.css
WebServer.cpp: no caching for css files.
controls.html: Add title to some buttons to clarify their purpose.