Avoid Code.eval_quoted in elixir dot-dsl

This turns out not to be needed.
Merge pull request #1191 from pminten/elixir-dot-dsl-improvement

Avoid Code.eval_quoted in elixir dot-dsl
Don't use newrelic in console
Add migration for user exercises.

Each submission for a language/slug belongs to an exercise. That hasn't
been explicit in the data model until now.
Write to (as yet unused) user exercise.
Update user exercise column on submission
Actually link user exercises and submissions
Optimize user exercise data migration
Tweak user exercise data migration
Don't use newrelic in rake tasks
Save language/slug on user exercise
Add index to user exercise
Don't link to W3Schools, they're not a good resource.
Refactor notification
Add a link to OCaml programming guidelines

These are quite helpful for a beginning OCamler.
Move nucleotide-count out of the way in Go
Merge pull request #1195 from pminten/add-link-to-ocaml-guidelines

Add a link to OCaml programming guidelines
Move point-mutations in go to the end of the track
Remove version count from submission
Delete unused method