Clean up warnings 1a

This is a modified version of the clean-up-warnings branch.  For this branch, model data is now pulled by LetterPageView instead of being pushed to it.  This eliminates the LetterPageView's dependency on Letter.  The test code was also updated and several checks for null were added in the application code so that all JUnit tests pass without any failures or errors.  Lastly, more warnings were cleaned up and duplicated test code was removed.

We still need to verify that everyone can run with Java version 7 (1.7).