new highscore layout and minor fixes

Please ignore the bin/, gen/, project.properties, .project and .classpath and use your own. Sorry, I now created a .gitignore.

* fixed warnings in some classes(unused imports mostly)
* added splash-dead.png for gameover.xml
* added pretty buttons in gameover.xml, activity_main.xml and about.xml
* exported strings from various .xml files into strings.xml