Include Java stack source

Include the UA Java stack source code instead of referencing a binary
that doesn’t actually exist in Maven central.

This source code includes minor, uncommitted fixes to bugs found at the
interop.
Approximate instance count of MonitoredDataItems
Implement FindServers service
Revise publishing intervals on subscription creation

Revise publishing intervals to no faster than 100ms. This should
eventually be configurable rather than hard-coded.
Minor improvements to UaNode implementations
Implement a minimum sampling interval on OpcUaNamespace nodes
Return Bad_NoMatch when no targets exist
Log-level tweak