Level magic numbers

[oldergod]

Overview

Magic numbers were used around level ids. I created 3 constants to be used instead as well as simplifying the way Level subclasses are instantiated.

[takahirom]

Thanks! 🔢 It became easier to read!

[takahirom]

Please fix this 🙏 e: /home/circleci/project/app/src/test/java/io/github/droidkaigi/confsched2018/presentation/sessions/feedback/SessionsFeedbackViewModelTest.kt: (47, 25): Too many arguments for public fun createDummySessionFeedback(sessionId: String = ...): SessionFeedback defined in io.github.droidkaigi.confsched2018 in file DummyDataCreator.kt

[takahirom]

LGTM 👍

[oldergod]

すみませんでした、対応しました。