Implement load balancing policies

[ZuzaOsa]

There are several implemented load balancing policies in the DataStax driver.

• RoundRobinPolicy
• DCAwareRoundRobinPolicy
• TokenAwarePolicy
• AllowListPolicy
• WhiteListPolicy

[adespawn]

With #326

• WhiteListPolicy will be removed
• RoundRobinPolicy, DCAwareRoundRobinPolicy and TokenAwarePolicy will be working. Identity of the behaviour with their old implementations remains untested
• New default policy is added