Cleanup project code

This covers a misc set of actions:

• enable warnings in maven compiler plugin
• fix warnings
• proper use of generics
• use of File.separator to prevent failures on Windows
• removal of System.out.println(..)
• misc typos
• removal of unused code
• use of PrivilegedAction for accessing TCCL and system properties
• set maven build encoding to UTF-8
• build at least at java 1.6 level