Update Changelog for the 0.8.0 release

[vitvakatu]

Overview

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See: https://jira.bf.local/browse/ECR-XYZ

Definition of Done

• There are no TODOs left in the code
• Change is covered by automated tests
• The coding guidelines are followed
• Public API has Javadoc
• Method preconditions are checked and documented in the Javadoc of the method
• Changelog is updated if needed (in case of notable or breaking changes)
• The continuous integration build passes

[MakarovS]

Sorry for late review, this was merged before I had a chance to look at it - but shouldn't we mention MerkleDb support here? Or does it fall under "internal fixes" from user's point of view and mention of Exonum 0.12 is sufficient?

[vitvakatu]

I thought about it, but it turns out that these changes are internal, there is no difference from the user's point of view (yet). We didn't move to MerkleDB, we just moved to Exonum 0.12 which (accidentally) has MerkleDB as one of the components.

So I think we should not mention that.