Collector aliasing should not be hard-coded

[salcock]

Collector aliases being hard-coded means that it is difficult for us to automate updates to bgpfinder when a collector changes names.

Things that need to resolved:

• collector aliases should be read from a database table, or from a file on disk.
• collector aliases should be regularly read from that source, so that any changes are picked up without requiring a restart of the entire service.

We don't have to check every scrape or served query; once per hour is probably more than enough to handle new aliases relatively transparently.