Implement an upgrade tool

[rafaelnajera]

The goal is to have a semi-automatic upgrade tool. The administration only has to upload an upgrade tarball and click an upgrade button in the user interface, without having to ssh to the server.

The upgrade script would do the following:

• Unpack and check the upgrade package
• Put the APM in maintenance mode
• Copy the appropriate files from the package
• Guide the user and upgrade the configuration file if necessary
• Guide the user and upgrade the database if necessary
• Put the system back in normal mode after the upgrade