Extract Subsystem tags from Mission Model

[Mythicaeda]

Prerequisite Issue: #928

When a mission model is uploaded, we need to extract the subsystems and put them in the tags table, as well as associate ActivityTypes with their subsystems.

Subsystems may be declared in one of two places:

1. As an @subsystem in the JavaDocs of an Activity (see Matt's work for extracting this information)
2. Statically, similar to how ActivityTypes are declared (not yet implemented, focus on 1 first)