add blacklist for memory store

[cvaliente]

the consumer configuration allows defining both a blacklist and a whitelist while the memory storage only has a whitelist. This makes it more consistent, allowing both consumers and storage to be configured with the same filter.

[coveralls]

Coverage increased (+0.04%) to 74.066% when pulling 74b309f on cvaliente:storageblacklist into fecab1e on linkedin:master.

[sam-obeid]

This is useful! +1

[vvuibert]

I tested this branch and it does not work me. Adding a group-whitelist in the storage section of the config file works, but adding group-blacklist has no effect.
The group-blacklist would be really useful though
(edit) this does work 👍

[bai]

Could we use negative regex in whitelist to achieve similar functionality?

[vvuibert]

@bai I believe that go doesn't allow negative regex and that is why we have a black list for the notifier and the consumer