Static Dictionary in Hub class

[Arman Forghani]

@pszmyd Thank you so much for this great module.

I have a problem. Don't you think using static readonly ConcurrentDictionary (in chat sample) causes problem for multitenancy feature in Orchard? I think in this case all instances of a hub class (through all tenant) use a shared dictionary to store users, ....

Do you recommend using CacheManager instead?