Instead, require an AndroidManifest.xml and always build an APK.

Fixes #2517

Well, all the easy ones, anyway.

For some reason `// ignore:` isn't working for me so I've disabled
lints that need that. Also disabled those that require a ton of work
(which I'm doing, but not in this PR, to keep it reviewable).

This adds:
- avoid_init_to_null
- library_names
- package_api_docs
- package_names
- package_prefixed_library_names
- prefer_is_not_empty
- sort_constructors_first
- sort_unnamed_constructors_first
- unnecessary_getters_setters

flutter start's method of finding devices to run the app on is not suitable for flutter drive.

This commit also refactors several tool services to allow mocking in unit tests.

Runs a test app and a driver test simultaneously, then stops the app.

Usage:

```
flutter drive --target=/path/to/test/app.dart
```

This command will look for `/path/to/test/app_test.dart` by
convention. We will expand into other ways of discovering tests in the
future.

Also, look for the Android SDK in the default locations.

The IOS code is totally untested. Need a Mac to test it.

Previously we'd always stop org.domokit.sky.shell. If an
AndroidManifest.xml exists, we'll use the activity specified in there
instead.

remove the device factory methods as well as the device cache

flutter start no longer depends on a pre-built SkyShell.apk. It builds a
new one, as long as an AndroidManifest.xml exists.

We rebuild the .apk every time either AndroidManifest.xml or
flutter.yaml changes.

rename to printTrace(), printStatus(), and printError()

Also improve the error message a bit if a download fails.

remove device type specific checks

Third-party libraries can now provide their own mojo services. They do
so by adding a config.yaml file to their pub package which contains
- a list of service names and java classes which handles that service's
  registration.
- a list of pre-built .jar files to statically link with the app's shell
  when building the app.

Fixes #1010