Change resource loading behavior

- letter.properties always loads from src/ dir and not from bin/ dir
- graphics file always load from src/....../Graphics/ dir.
- sound find continue to load from bin/..../Sounds/ dir

There are some issues when I tried to change sound file behavior too.
Have not looked into it yet. But things seem to be working. Now my
updates to letter.properties file are visible on application relaunch
and one does not have to clean project, rebuild it.
Merge pull request #30 from CS673/vivek-model-fixes-3

Change resource loading behavior