Add versioning to initiatives
**Is your feature request related to a problem? Please describe.**
Currently an admin can apply all the changes it wants to an initiative. There is no way to track these changes. It's not transparent.
**Describe the solution you'd like**
We should have a versioning system for petitions like we have for proposals and results.
Changes that should be tracked :
- Text changes to title, description and hashtags
- State changes
- Changes in authorship (especially track co-authors)
**Describe alternatives you've considered**
**Does this issue could impact on users private data?**
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