Update BoardGen.java

Lots of changes. Sped up the board generation by a lot by creating the random and calendar objects ahead of time instead of every time. Pretty much rewrote boardgen.java. Created a method that would rotate the board based on a randomly chosen number. The current total possible boards, without counting the randomly removed items is now: 4*4*4 = 64, with the randomly removed 10 digits the possible total of games should now be in the thousands. When I have time I'll add in more boards generating a possible 12*4*4 = 192 boards not counting the removed items. Tried to keep board generation mainly private besides the main method of creating a board and then retrieval of data.