ACCUMULO-2615 Refactor server configurations

* ServerConfiguration is deprecated in favor of the new ServerConfigurationFactory.
* ServerConfigurationFactory caches configurations not just but namespace or table ID, but
  also by instance ID.
* ZooConfigurationFactory takes over the creation logic from ZooConfiguration. A
  ZooConfiguration instance is no longer a singleton, but an ordinary instance.
  ZooConfigurationFactory caches created ones by instance ID.
* NamespaceConfiguration and TableConfiguration each keep a static map of ZooCache instances,
  rather than a single static instance. The map is keyed by instance ID and namespace/table
  (resp.) ID.
* getParentConfiguration() was added to all appropriate configurations.
* The logic for retrieving properties from ZooCache instances is refactored to a new
  ZooCachePropertyAccessor object.
Merge branch '1.6.1-SNAPSHOT'

Conflicts:
	server/base/src/main/java/org/apache/accumulo/server/conf/NamespaceConfiguration.java
	server/base/src/main/java/org/apache/accumulo/server/conf/TableConfiguration.java
ACCUMULO-2615 Update Constants.UTF8 to StandardCharsets.UTF_8 for 1.7.x+