Bump to -SNAPSHOT version

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

The required updates (apart from nexus-staging-maven-plugin's because it
is in a profile) were pointed out by: mvn versions:display-plugin-updates

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