add: detect manual mining pool prioritizations

[0xB10C]

Pools, like for example ViaBTC, are known to manually prioritize transactions based on out-of-band payments.

For example https://miningpool.observer/template-and-block/00000000000000000005bc18c9903efcd39f6a972fb1df4eb843617f6af71b90

This can be detected and annotated with, e.g. block tags.

[0xB10C]

This get's a bit easier with #72.