New module: Upgrade

Added new functionality to upgrade MADlib deployment on a database without
removing the previous installation. This is currently only supported for version
0.5 and greater. We don't yet support upgrade in Postgresql systems since
MADlib installs a Bool-to-Text cast in Greenplum and the upgrade tries to drop
the cast. This leads to a problem in Postgresql and should be handled as an
exception in future releases.
Correlation: Ensure duplicate target column names are handled

Other changes:
- Updated help message to reflect changes in output table format
- Updated output message before correlation is started
Release v0.7 tasks: Update version, add release notes and tags