add next level load upon level completion

after a level is completed the next level will be loaded
two new functions have been added:
*level_first that loads level one, or creates a random level,
 if file is missing
*level_next that loads next level, and if no level file is available
 a random level is created, also if MAX_LEVEL is reached (set to 10)
 then level first will be loaded again.

once a level is complete then level_next is launched

closes #3