JUnit Testing is now implemented

Grading JUnit tests is not yet implemented.
Junit Jars are now stored with relative location
Renamed unit tests to simple unit tests (because soon there will be JUnit tests as well)
Now tests JUnit tests as well as Simple Unit Tests
Updated build script (hopefully that fixes the build server)
JUnit Tests can now be added similarly to Simple Unit Tests
Fixed not showing folders in file browser.
Updated dropbox api.
Added slightly better error logging (stack traces on stack traces on stack traces).