Add vhost name based activation strategy

The activation strategy that will use the Virtual Host (vhost) server name
used in the request to decide if the feature is active or not.
This strategy can be useful when given service instance is available through
two different Virtual Host names (vhosts like www.example.com and
beta.example.com) each with different features enabled.
By the way test dependencies update and unification.

I left one TODO - support for wildcard in domain name (like *.beta.example.com).
I don't use it and it would be rather rarely used. Nevertheless, if there was a demand
for this feature I could implement it.

Btw, I had problem with a name for this strategy. The current one sounded sensible
for my colleagues, but maybe you will have an idea for a better (more meaningful) one.