Design/Prototype for Data Adapter storage

As a Graylog user, I want to take advantage of threat intel streams that are distributed as large data sets without having to keep all of the data in main memory.

# Input Criteria
- [x] Basic requirements for threat intel data streams known

# Output Criteria
- [ ] Technical path forward identified for handling data from bulk-download threat intel streams
- [ ] Prototype code written to demonstrate

# Tasks
- [ ] Design a mechanism for storing and utilizing data sets from bulk download sources (likely MongoDB)
- [ ] Discuss design proposal with team (include Bernd)
- [ ] Implement proof-of-concept code to show that the approach works