Fix test in clojure ETL exercise
clojure.string/split was including an empty string as a letter

For some reason perhaps only known to Rich Hickey, `(clojure.string/split
"abc" #"")` evaluates to `["" "a" "b" "c"]` (i.e. includes an empty
string). I don't think this is what we want for the ETL test - and in fact the
current example solution does not pass the tests for this reason. I've
updated the tests to use `re-seq` instead, which gets us the letters
minus the blank space, and I've simplified the example solution a little
as it didn't need nested for loops.
Merge pull request #1187 from rsslldnphy/fix/clojure-etl

Fix test in clojure ETL exercise
Fix admin section
Fix dot-dsl README. Fixes #1183.
Add Elixir forth exercise
Reorganize app endpoints
Fix redirects and links in admin
Simplify convenience methods
Add dynamic list of upcoming languages
Merge pull request #1188 from pminten/elixir-forth-exercise

Add Elixir forth exercise
Roughly organize views
Fix broken link
Merge pull request #1190 from slava-sh/master

Fix broken link
Simplify space age example. Fixes #190
Add a couple of database indices
Collapse db migrations
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.