maven 3 warns about blueflood.version so remove it

Maven3 warns about all our versions being expressions instead of static,
so switch to static versions numbers. Follow the same pattern as
dropbox:
https://github.com/dropwizard/dropwizard/blob/master/dropwizard-configuration/pom.xml

We can use the maven versions plugin to change the versions on
everything at the same time.