A bunch of small changes, but mostly making writingfield work with Grappelli

Hi,

here is my potential contribution to `writingfield`.

Some of my changes are purely cosmetic (font size, padding, saving string, etc), but the most interesting part is the **form compatibility with Grappelli**. 

I didn't saw the other pull request at first and I also fixed the `<a class…` to make the button visible again.

Other small things (shortcut for FS activation, protocol agnostic `Media`…) can be reviewed individually, I tried to make patches as small as possible.

thanks for `writingfields` and best regards,