Drop Scala 2.11 (and 2.12?)

[mkurz]

Anorm still supports Scala 2.11. The last 2.11 release was in 2017.
I think it's finally time to move on...
By dropping Scala 2.11 the build setup could be much more simplified.

Even dropping Scala 2.12 should be considered.

[gaeljw]

Dropping both 2.11 and 2.12 make sense to me. (In a minor version I guess?).

From what I see in my company, 2.12 is still used only for Spark apps (and even there, it's eventually moving on!). 2.12 could make sense to be kept if we think Spark apps are likely to actively use Anorm but I don't think it is.