Add benchmark for Dart.

This is a work in progress.  See TODO.txt for what work remains.
Don't gitignore pubspec.lock.

Apparently application packages should have pubspec.lock in source control.
http://pub.dartlang.org/doc/glossary.html#lockfile
Update dart dependencies and TODO list.
Update dart readme.
Make dart setup file use nginx as a load balancer.

This script is untested and almost certainly contains bugs.
Modify the benchmark installer to download the dart SDK.
Update Dart TODO list.
Merge branch 'dart' of gitlab.techempower.com:techempower/frameworkbenchmarks into dart
Add dart to PATH
set sort order and fix setup file