GitLab

- validate image metadata format
- read metadata from file
- merge file-loaded metadata with runtimes
- store metadata file on pithos, check existance, overwrite with -f
- raise helpful error messages when there fail

Refs: #3797

Parse ivalid property file and guide users to correct it
Guide users to pass valid container:path parameters

Refs:#3769

Unsolved bug: redudant info in logfile

Feature #3566

The client is still called 'astakos', but the command group is now 'user'

Feature #3566

This typo caused undesired behavior when deleting a deleted network

Bug #3547

Concerns store_copy operation and aims to clean up the code that
implements the account-to-account copy

So far tested in astakos only