Who takes the decisions of "hard-forks" in the Bitcoin community? I understand that there is no central authority on Bitcoin, but I can't understand who takes decisions on "forking" the blockchain.

Here it was mentioned that the "Bitcoin community voted"—how did that happen? Who is the community? I assume anyone? If so, how can one vote? 

I was reading about a hard-fork coming on 16th of November and I don't really understand how that works.
No-one decides literally for everyone. Miners make the decision to exploit one proposal rather than another one, so whenever miners disagree and don't follow one protocol to around 100% then a fork happens. 

In this case (of B2X) it is the proposal of Segwit2x that will or will not be followed.