Add level 9.

This will probably be level 3 in the final version.
Add level 10.
Add level 11.
Add level 12.

This will probably be moved earlier. This level will seem familar to
those that have tested this game a lot :)
Delete the test level.
Add level 13.
Add level 14.
Add level 15.
Add an extra attempt to level 6.
Change a platform's position in level 8.

This makes it harder to beat the level with only one ball.
Change the order of the levels.
Remove placeholder text.
Merge remote-tracking branch 'jorenz/new-levels-two'