* makes per-build entries in per-app entries
* `fdroid scanner --json --verbose` will output logging messages to stderr
* removed " at line N" from one message to make them uniform keys
* this will be used in issuebot
This is a second attempt with tests for how `fdroid build` calls the
scanner functions. closes#771. It was previously merged in !748 then
reverted in 68c072c72e