refactor(ajax): rename handle-ajax to ajax/perform-request

- rename handle-ajax.litcoffee to ajax/perform-request.litcoffee
- accept app as an argument instead of requiring it inside
- update ajax.litcoffee and background scripts accordingly
fix(ajax): remove ".template." from test/unit/ajax.litcoffee
refactor(vkApi): move vk-api-auth-helper to vk-api/

Rename vk-api-auth-helper.litcoffee to vk-api/iframe-auth-helper.litcoffee
chore(meta): bump version to 0.4.0