Replaced absolute paths to the components with relative ones.

[KOLANICH]

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Fixes: #254

Description of the changes being introduced by the pull request:
Importing stuff from an own package by its absolute name is harmful. It causes problems with forks using other names. So I have replaced absolute imports with relative ones.

Please verify and check that the pull request fulfils the following
requirements:

• The code follows the Code Style Guidelines
• Tests have been added for the bug fix or new feature
• Docs have been added for the bug fix or new feature

[coveralls]

Coverage decreased (-98.9%) to 0.0% when pulling bdccf48 on KOLANICH:fix_import into c94fcf7 on secure-systems-lab:master.

[joshuagl]

Whilst I appreciate the suggestion, I'm not convinced this is a change we want to take in securesystemslib. PEP 8 recommends against this style of import unless necessary, and I'm not convinced it is necessary.

Are you aware of a fork for which this import style is causing problems? Can we encourage them to work with us, rather than forking?

[KOLANICH]

I don't know any fork it really causes problems to (I haven't searched for any forks), but using absolute imports are making issues from thin air. It not only creates problems for forks, it also creates problems for us. Code using absolute imports is harder to refactor.

[joshuagl]

Thank you for the submission! Whilst we are very grateful for the contribution we have decided not to merge this PR. We like following the ecosystem norms as defined in PEP 8.