206 scalafmt is messing up diffs too much

[nawforce]

This adds sbt-scalafmt so we can use sbt scalafmtAll to update formatting quickly. I have also added sbt scalafmtCheck so the CI build should fail if we have not got scalafmt setup correctly when making changes.

The build changes are in the first commit, the second has reformatted sources.

[pwrightcertinia]

I am not sure why the plugin is necessary if it will be run separately to the build - you can run scalafmt on its own with the same features I think. It's now possible to integrate it into the build tasks at the beginning, but it might slow things down a bit.

I am planning to replace the existing git hook contents on the other repos with lint-staged so it can run all the different types of formatter if needed. I realise this repo does not have much of a js presence, so I can see why we might use a different way here.

[nawforce]

I don't have scalafmt installed as a command line tool, I just use InteiliJ to take care of this. I could reformat all files that way but having a block in the build appeared important which looked to me like easier done via sbt plugin. I can drop those changes if you prefer and just correct all the errors, I have a PR open where I can't see the changes clearly because of the number of formatting changes. Github ignore whitespace helps with some but there are still quite a lot left.

[pwrightcertinia]

Actually I've changed my mind - scalafmt is not available (on PATH atleast) by default in CI like sbt is. So this is decent, it wouldn't interfere with anything else either so no harm done. Sorry

Could be nice to run it as part of build, flip between check/all depending on CI=true environment