Move all static state into Client Context

As a follow on to #718 it would be nice to move all static state into Client Context and have a single Client Context object per an Accumulo Client. For compatibility, Connector could have a static map of Client Context objects. For sever processes, there should only be one instance of ServerContext that is used for the entire process.

Review the changes and discussion from #718, then trace Client Context, Connector, and ServerContext usage across the project. Define how one Client Context maps to each Accumulo Client, how Connector preserves compatibility, and how server processes share one ServerContext; done requires all static state to follow that model.

Written by the indexing model from the issue text.