Add command to organize old plugin version packages

[Xpirix]

• This PR is for this issue: #327

Changes summary:

The command runs the following process:

• List all plugin versions created before 31 December 2014 that are located directly in the folder packages
• Create a folder according to the created_on year and move each package inside it
• Update the package field in the PluginVersion model

To run the command: python manage.py organize_old_package

[dimasciput]

@Xpirix, could you change the 'move' command to 'copy' instead? Then, we can delete the duplicates after we've ensured that everything is good

[Xpirix]

Thanks @dimasciput , I've converted this to a draft for the moment. We also need to ensure the coverage of the backup script with @timlinux before running this command on the server side

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (b661773) 32.51% compared to head (e8592d8) 82.75%. Report is 8 commits behind head on master.

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #328 +/- ## =========================================== + Coverage 32.51% 82.75% +50.24% =========================================== Files 71 142 +71 Lines 4217 5497 +1280 =========================================== + Hits 1371 4549 +3178 + Misses 2846 948 -1898 ```

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