Small miscellaneous changes

• By opening this merge request, you agree to release your code and all other changes under the GPL 3 license and to abide by the terms set by this license.
• Migrations have been added if applicable (migrations are always necessary for removing/renaming item asset files)
• Significant changes of this merge request have been added to the changelog.

---

Changelog

The format is based on Keep a Changelog.

Added

• Disclaimer in the changelog to remind people to use periods and so make style consistent.

Changed

• Refactor .gitignore.
• Refactor the changelog.
• Update donation URL in the README to make it consistent with those on the Veloren website.
• Update a minor technicality in the README.