adds possibility to load level from text file

added level.txt that is a level that can be loaded with L key
level is loaded from text file level.txt inside folder levels
text file format is 20 rows and 24 lines
each character represents a brick:
 - 0 for no brick
 - 1 for normal brick
 - 2 for dual brick
 - 3 for triple brick
 - 9 for superman brick