Minor version pinning

Warning: YAGNI material ahead. Just capturing some thoughts.

We have several libraries we pin — currently servlets, JSP, and Objectify — because the latest version is not appropriate for all environments.

We implicitly assume we can pick a specific version -- e.g. Servlet 2.5.0, Objectify 5.1.22 -- and that this will not change going forward. This may not be true. For instance, there could be a 5.1.23 of Objectify that fixes bugs for the old library.

We could make our pinning less fixed. E.g. we might want to pin Objectify to the latest version in the 5.x range, or the 5.1.x range.

Not worth working on unless this actually happens.