Add a BridgeDB module

While talking about making a PT infographic and interesting stats to point out, asn pointed out that there are no publicly available BridgeDB stats.

This can be useful in many different fronts, such as seeing the balance between usage and available resources.

This ticket is about adding a CollecTor module that will archive the stats exposed in legacy/trac#9316 (moved). The actual stats and format should be discussed in legacy/trac#9316 (moved) and may benefit from the discussion in legacy/trac#29315 (moved).