Switch to supported versions of runtime dependencies

[karlmdavis]

Haven't touched this project in over two years, but would now like to get it deployed to production again. Unfortunately, in order to do that I need to get it running on a platform that hasn't been EOL'd. More to the point: I need to get it running on things that I can easily install and maintain on Ubuntu 16.04.

So far, that looks like:

• Switch from Java 7 to Java 8 or 9.
• Switch from Tomcat 7 to Tomcat 8.
  • Just checked, and this is option: Ubuntu 16.04 has packages for Tomcat 7.
  • Specifically, Ubuntu 16.04 has v8.0.32. Per https://tomcat.apache.org/whichversion.html, that version:
    • Is EOL'd in favor of v8.5.x and 9.x. (Of course, that's the project's policy -- Ubuntu/Debian do still support it.)
    • Doesn't have HTTP/2 support.
    • Doesn't have SNI support (which I don't need, as Apache HTTPD is handling SSL).
  • It's probably still a good idea to switch, though.

[karlmdavis]

Resolved in PR #112.