Power up lock

add lock and unlock features. at the beginning only level 0 is unlocked, if the user finishes level 0 level 1 will be unlocked.

NOTES: i have a test flag in levelviewcontroller, if test is on, all levels should be unlocked
TODO:  currently an array of lock levels are stored between levelviewcontroller and gameviewcontroller, which means if the user goes back to menuviewcontroller, the all levels except level 0 will be locked again.