CHANGELOG for version 0.7

1. Clean up CLI error handling code
2. Unify and improve data size units presentation
3. Ask for user permission at store-delete
4. Intuitive semantics for store-move/copy/download/upload (modified syntax and clients)
5. Dynamically limit max number of threads
6. Cache user info in astakos client
7. Use UUID instead of email in pithos client calls
8. Organize client unittests in a package and update to comply with new synnefo specs
9. Allow character : in container operations in store interface