Feature/conference refactor

**Work in progress; not ready for merge**

# Purpose
The conference submission service is largely untested. It's also currently hard to test, since it's mostly made up of a few large functions with many responsibilities. This patch refactors the existing code into smaller, most testable units, and tests those units.

# Changes
* Refactor conference submission logic into helper classes / functions
* Test refactored code

# Side effects
None expected
Because TokuMX throws errors when we try to do a write that updates both array indices and non-array indices. Since `Node` has both types of indices, trying to save when changing `system_tags` crashes. I honestly don't understand how this ever worked in the first place, but I first encountered the problem locally after upgrading to TokuMX 2.0 and haven't been able to fix it since.