Default care card heading level

[the-nathan-smith]

I've added the ability to alter the default heading level for care cards. This is done with the addition of a new setting. If the setting is not present within a project, the default heading level stays the same (3), thus not affecting users who do not wish to change their default.

[DomBaker]

Just one more thing needs doing - update CHANGELOG.md 👍

[mikemonteith]

Just one more thing needs doing - update CHANGELOG.md 👍

You'll want to add some documentation under ./docs too as well as a note in the CHANGELOG

[mikemonteith]

I merged this on the command line because I squashed commits into 1 commit. I thought github would be clever enough to realise and close it as successful merge but it didn't 😢