model: Alphabet: Fix string comapre function
model: sound: Get sound resources from src/ dir like image

- Bring sound resources inline with image and letter.properties
- Soon it will be changed to read from a temp dir created for resources
- Also used BufferedInputStream to fix an exception problem.
Do not modify files in "src" directory

There are multiple cleanups in this patch.

- Do not change current working dir.
- All resources are copied into persistent_dir/ and all modifications
  happen in that directory. src/ directory is left untouched. This
  should allow running app from jar file.
model: Fix directory path for loading persistent resource
Merge pull request #45 from CS673/vivek-iter3-model-fixes

Vivek iter3 model fixes