Update FileUtils.java

Fixed a bug that was causing Gson to throw EOF exceptions.
PersistentHashMap's remove method works properly now.
Updated TestPersistentHashMap to properly test isEmpty
Made FileUtils slightly more testable
Started a test for FileUtils

Created a test for the getStringFromReader method, seeing there was an issue with that specific code before.
Merge pull request #1 from Joe0/master

Completed TODOs and fixed a bug