Added support for Inverse references

Null string instead of string of 0 length for null QualifiedName and LocalizedText
This is what uaexpert does, so it is probably correct

SQL History storage

Add interface for SQLite
Pass history interface node instead of node.nodeid
Add storage.stop() method for future

History fixes and event support WORK IN PROGRESS

This reverts commit 6069acb1.

Server history support for DataValues (Not events)