Modified buildRandomCharBoard() to use a double for loop instead of a
single for loop with index conversion.
Fixed a typo in buildRandomCharBoard() that was causing a bounds issue.
Also moved some methods around for organization.
Completed the testFlipVertical() in BBOperatorsTest.java
Completed testFlipHorizontal() in BBOperatorsTests.java.
Completed testIntersection() in BBOperatorsTest.java
Completed testUnion() in BBOperatorsTest.java
Finished testNot() and made some name changes to testUnion() in
BBOperatorsTest.java
Completed testIsASubsetOfB() in BBOperatorsTest.java.