Unify css

Hi!

Being a long-time Shaarli user, I've started to work on my own stylesheet; doing so, I stumbled upon some inconsistencies within the default CSS:
* mixed used of tabs and spaces
* presence of trailing whitespaces and empty lines inside blocks
* unclear indentation / coding style
** spaces around curly brackets (block declaration)
** spaces around CSS attributes
** unreadable one-line declarations
* comments in French
* duplicate / overriden declarations (e.g. padding values for `#linklist li`)

The attached commits provide a unified coding style, as follows:
```css
/* one-liner */
elem1, elem2 { attribute1: value; attribute2: value; }

/* longer declaration */
elem1 subelem.subclass elem2 {
    attribute1: value;
    attribute2: value;
}

/* specific displays */
@media print {
    elem1 { attribute1: value; }

    #id1 subelem, elem3 subelem.subclass {
        attribute: value;
    }
}
```

Feel free to comment on the (in)utility of this feature, I'd be happy to take any suggestion into account!
Note that the commits can be squashed / expanded if needed, depending on your preference for commitlog atomicity or concision ;-)