Add ability to set many remote candidates at once

[mickel8]

In this issue ability for setting many remote candidates at the same time should be added.

There exist message {:add_remote_candidate, candidate, stream_id, component_id} which set one remote candidate. What we need is to add support for message {:add_remote_candidates, candidates, stream_id, component_id} to parse many candidates for specified component in specified stream.

If we were able to pass structs in Unifex we could even add support for message of format {:add_remote_candidates, candidates} where each candidate is represented by structure containing following fields:

candidate_sdp
stream_id
component_id

But this is out of the scope of this issue.