The per-series settings aren't quite functional yet, but they're also
accessible outside of the sheet.
(cherry picked from commit 28131ac1357e1134d75c02e2a3bb5e3161a3ecfe)
# Conflicts:
# app/src/main/java/eu/kanade/presentation/reader/settings/ReadingModePage.kt
# app/src/main/res/layout/reader_activity.xml
# app/src/main/res/values/attrs.xml
# app/src/main/res/values/themes.xml