Add automatic header creation on compilation

[oleg-py]

First step to finishing #513.

There's sbt-header just for making headers on files, so I decided to put this together.

I ran the headerCreate command on whole project and it only touched few files where the header was outdated. I also set the project in the way that doing sbt compile will automatically create headers, so the contributors are not bothered by it. Alternatively, it could be made so that users have to run command manually and CI fails build if header is not correct.

Of other formatting tools, it seems that only Scalastyle has the header check, but I haven't looked into formatting tool yet, so I decided against committing to Scalastyle for now.

[codecov]

Codecov Report

Merging #531 into master will increase coverage by 0.05%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #531      +/-   ##
==========================================
+ Coverage   90.38%   90.43%   +0.05%     
==========================================
  Files         362      362              
  Lines        9610     9610              
  Branches     1802     1802              
==========================================
+ Hits         8686     8691       +5     
+ Misses        924      919       -5

[alexandru]

Oh, nice, thanks.

[dwijnand]

Btw sbt-header has headerCheck which you can invoke in CI to enforce headers.

https://github.com/sbt/sbt-header/tree/v4.1.0#checking-headers