Replace all fonts with ones that are shipped with Performous. No more Microsoft dependency.

- New Rocker (blackletter), Droid Sans Mono (monospace) and Goblin (serif)
- Goblin renders in larger size than other fonts, this may need to be adjusted for in theme files
- Quickly reviewed for graphical bugs but needs more testing
Make the text in song selector a little less broken.

- Centered
- Do not append menu usage if there are no songs (that match search)
- No newline in "Visit performous.org ..." (l10n not updated)