Before this commit we used to fetch the whole journal entry list in one
go, which caused issues in two cases:
1. On slow internet connections the download may fail.
2. With big journals: Android interrupts sync managers if they don't
perform any significant network traffic for over a minute[1],
and because we would first download and only then process, we would
sometimes hit this threshold.
Current chunk size is set to 50.
1: https://developer.android.com/reference/android/content/AbstractThreadedSyncAdapter.html
We were not detecting the version correctly, but always just assumed
latest version, which is obviously wrong.
In addition, before this commit we used to automatically verify on
fetch, which wasn't flexible enough for some use cases. This fixes that
too.
If a journal has a key set to it (usually used for shared journals), use
it instead of the symmetric key. The key of the journal is asymmetrically
encrypted using our keypair.
