Update list of changes since last release in the CHANGELOG

[romaricpascal]

I think I collected all the revelant pull requests merged since the last release.

Closes #624.

[romaricpascal]

@claireashworth Looks like I missed a couple of things for the breaking changes, sorry:

• the PRs leading to the polyfill breaking change (thanks @colinrotherham for making me notice, do other PRs need to be added for that one?)
• the PR for the changes of styles which may lead to services needing to do some minor CSS tweaks (so I've put it in breaking)

Would you be able to give another look, please? 😊