* Drops support for mocking the frontlight setting internally which may
cause incorrect in-memory values.
* Adds new supported value for `KOBO_LIGHT_ON_START` (-2), which sets
'Kobo eReader.conf' as the source to update `settings.reader.lua`'s
brightness setting on startup, thus using the value from it
indirectly.
* Adds the `KOBO_SYNC_BRIGHTNESS_WITH_NICKEL` configuration variable
which updates 'Kobo eReader.conf' every time the brightness setting is
changed within koreader.
* Fixes missing call to save brightness when modifying via two-finger
swipe.
Closes#1523.
eb47c5a39f