Add simple python server

 - rewrites requests for flat files to .html
Move and rename stub server file
Feature tests!
Merge branch 'master' into end_to_end_tests
Newline at the end of file
Return 404 for non exsistent files
Test for page existing on master branch
Merge pull request #6 from alphagov/end_to_end_tests

Awesome, thanks @maxfliri