Override underlined links in button text

* Added "text-decoration: none" to button text;
* css file is loaded in the options page, too. Now the preview is displayed correctly.
* css file now is generated only on options update (used to be every time the options page is opened).
Explicitly declared a global variable (array of default values)

This fixes bug https://github.com/ciubotaru/share-on-diaspora/issues/19.
Merge branch 'button-css' into unstable