Break application tab to application projects

[tzach]

Currently Cassandra tab code is part of the osv-gui, regardless of the availability of Cassandra application.
This have a few drawbacks:

1. GUI code need to dynamically check if Cassandra is available (this is known at build time)
2. GUI code will bloat with each new application and application tab
3. Adding new application require update to the core osv-gui project

A correct solution will put the Cassandra tab under application Cassandra.