Diff command implementation

[alexmaslenn]

Implementation of diff command for Topology Templates
Currently works on Template, not Instance level
https://github.com/xlab-si/xopera-opera/tree/diff-update

Connected issues #138 #130

[dradX]

Excellent @alexmaslenn! As we discussed before we should also support the instance level diffs. But I find the option to calculate template diffs very useful.

[anzoman]

#147 has been merged and the dev opera release is already available on Test PyPI instance.

[anzoman]

I want to add an additional question - will we also extend the support for opera diff and update commands to work on (compressed) TOSCA CSARs or is that not a current priority?

[alexmaslenn]

Yes we will.

[anzoman]

#156 has been merged too. The newest opera update command is available within the latest opera pre-release on Test PyPI here: https://test.pypi.org/project/opera/0.6.4.dev8/.

[anzoman]

Both opera diff and opera update commands are now implemented and available in the latest opera version - 0.6.4.