Fix default level of StderrLogService

Actually, we fix it in AbstractLogService which failed to transport
the default level behavior from StderrLogService.

Pointed out by Curtis Rueden.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Test the default level with StderrLogService

To prevent future regressions.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Bump to next development cycle

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>