Updates

- Changed GoogleTest and GoogleProtobuf to use package source
  from cached directory rather than download everytime
- Made lag-build parallel ( -j4 )
Adding support for Google Protobuf

- Necessary structure for generating proto headers and compiling
  proto sources
Adding support for Google Protobuf

- Working model for Googlr Protobuf enabled library and executable
- Minimum cmake version moved to 2.8.12 to use more latest target_include_directories
- Changed signature of generate_proto_src in opt-googleprotobuf.cmake to be more generic