Update game_manager.js

Added functionality to add "fake" move count to the move counter.

For eg, if the user asks for tile 16, the maximum moves needed to score a 16 is 7. Now, 7 will be added to the total number of moves made for authenticity.
That is,
2*2 = 4 (4 moves)
4*2 = 8 (2 moves)
8*2 = 16 (1 move) 
Total = 7 moves.

A random factor is added, in order to account for direct 4s, or multiple combinations in a single move.
TODO: Can be refined