closes#517
add index test for Application
add app.toJSON test
add test for app.inspect()
add tests for app.use()
add tests for app.onerror()
add tests for app.respond()
add tests for app.context()
add tests for app.request()
add tests for app.response
refactor for non-existence of test/app...js
no need for *.js
use helpers/ dir for non-tests
