Compress the CSS in css2js.js, by removing comments & indentation

The file webodf.css is currently more or less directly converted into a string by css2js.js. Including the license header, all other comments and the indentation.

Based on heuristics and my little CSS syntax knowledge (so please better check) I propose to do some simple compression when creating the string. Spares some 5K bytes on webodf.js

Name | Size Before | Size After
--------|----------|-----
webodf/webodf.css.js| 16288 | 10929
webodf/webodf.js| 355267 | 349908

Fixes #785
If you choose to keep the existing regexps, is there a reason you use ``[ \t]`` rather than ``\s``?