Ember FastBoot v2 integrations

This issue serves to detail proposed changes to ember-cli-fastboot that seek to improve developer ergonomics while ensuring the fastboot-app-server is extensible and flexible. The plan is to pull in changes from these two repos.

- https://github.com/snewcomer/ember-alt-fastboot-app-server
- https://github.com/snewcomer/ember-cli-integrated-fastboot

Some additional considerations:

1. Running `ember serve` should use your fastboot-app-server configuration and not a faux app-server. This will help you avoid shipping bugs to production.
2. https support in development
3. See https://github.com/snewcomer/ember-alt-fastboot-app-server#general-design

These proposed changes do not suggest production facing enhancements related to the FastBoot pkg.