Move ICE servers retrieval inside the SDK and out of Olympus

[atsakiridis]

Right now the ICE servers are retrieved during sign-in, which is good as a caching mechanism, but I'm afraid we might have issues if ICE servers need to be updated, or if they are short lived (depending of the policy of the configuration URL server)

Another issue is that we make it more complex for the App developer to integrate with SDK, and we are inconsistent with the mobile SDKs where ICE servers retrieval happens at the beginning of each call. This does introduce a performance hit, but so far it's not noticeable.

So let's focus on getting all SDKs consistent and later down the road we can consider caching policies.