added MBFileManagerTest class and necessary resources
created test cases for MBFileManager
Added all code files to Test Bundle target, disabled ARC for the test bundle target and added linker flag "-lz" to support libz usage
cleaned up code in MBFileManagerTest
MBFileManager now does not add .xml extension to filenames. Changed MBFileDataHandler accordingly.
changed default filename strings (added .xml extension)
Merge pull request #31 from sven-m/feature/MBFileManager-XML-extensions

Feature/mb file manager xml extensions