Add scalafix

[mdedetrich]

Scalafix is an official EPFL scala plugin that lets you do many inspections that is normally delegated to Intellij such as

• Adding types to public members
• Organizing imports (since it uses the actual scalac compiler its not going to have false positives/negatives)
• Remove unused val's that are not referenced

The nice thing is that since this is just an sbt plugin, all of these inspections are not tied to an IDE. Furthermore we can actually check that the code has scalafix applied on CI to prevent it from rotting over time.

As with the scalafmt PR, if there any issues with the config let me know and I can change/rebase PR.

Note that I plan to document this in an upcoming future PR that adds CONTRIBUTING.md

[mdedetrich]

@raboof What are your thoughts on this? Its the last PR I want to do on the bucket list of "things to make project easier to maintain" before I start getting to work on real features.

If you feel apprehensive on this for now then its fine, I can close the PR and/or reopen it for later (note in the worst case scenario if something happens later we can always just disable scalafix)

[raboof]

Let's remove ExplicitResultTypes and then merge, see how we like it.

[mdedetrich]

Let's remove ExplicitResultTypes and then merge, see how we like it.

Okay will do, sec

[mdedetrich]

@raboof Done, rebased and pushed the PR. Without ExplicitResultTypes the diff is definitely a lot smaller.