Avoid crash if config.start_secure_session not defined

This config variable is set in the moj_peoplefinder app, but not defined
when running tests using the dummy app.

It might be cleaner to make this a config setting on the engine, but
just doing something to get this working and prove the engine approach
for now.
Ensure valid_login_domains is robust
Ensure unset ga_tracking_id does not break
Update git ignore file
Adding gemspec reference to Gemfile
Update Rakefile
Generated engine boilerplate
Mount the engine at /

some of the tests have hard-coded expectations about urls generated, so
we need to mount the engine at / otherwise the generated urls will
differ from those expectations.
Configure dummy database
Move gem dependencies into gemspec
Correctly require rspec and other gems needed for testing
Correctly configure test helpers
Ignore dummy uploads
Remove dummy layout, css and js files

they mask the ones from the engine, which we don't want
Ensure that vendored components are on asset path
Remove peoplefinder specific css

the upper level application.css is the one which gets pulled in from the layout
Move javascripts into peoplefinder subdirectory
Correct vendor asset path (for engine)
Remove unused rack-timeout

it was added in order to test asset uploads on heroku, but not needed any more.
Remove configuration files

(which are relevant only to the wrapper application)