* export to xml based on namespaces

* cleanup of ua_utils.get_nodes_of_namespace

* fix export Enum and custom datatype variables

* fixed extensionobject export again (removed typo)

* Test for import/export EnumValues

* move XmlExport.get_variable_basetype to ua_utils.py

* undo cleanup of get_variable_basetype

Can't check 'not val' because variable nodes with a value of 0.0 don't
get exported.

* do not create Variant with value None when they are supported by protocol

* add get_default_value to uatypes. This will be usefull at several places like opcuamodeler

* set correct default value in high level type creation method

* Made subscribe handle most iterable items 

like dicts, etc

* replaced try/except with isinstance

* Improve instantiate when parent has string node id

* Make String node id instantiation more clear

* Fix string to value for boolean

Can't use bool(string); will always return true
Make string to UA ints more readable

* Ignore XML Extensions tag

Other modelers make this XML element which contains a model and hash
from the generation tool

* Add test for instaniate with String NodeIds

* Handle import of Null values

* also export namespace of referenced nodes

* xmlexport: also export ns used in browsename

* __str__ for NodeData

* heavy cleanup of xmlimporter

* more xml import fixes

* fix importing lists of primitives

* export and import array dimensions

* fix by-ref error

* remove debug print

* fix xml test

* do not store ns uri when not necessary

* sdfsdfsd

* Guid as a primitive

UA Guids based on python UUID type

* Guid primitive fixes, import datetime

* Fix Guid NodeId, typos, tests

* Add guid test, python 2.7 fixes

* Guid fixes for modeler

* Pep fixes for edited files

* Fix pep refactor

* Remove string check for datime/guid

this function assumes correct value is supplied, update doc string

* - added tools/uacall script

* As suggested by oroulet corrected misunderstandings in signature of
Node.call_method(). No parent needed, just use self.

* Old folks, knowing Python2.x only, keep forgetting that print should
have been a function in the first place...

Added support for Double and Float value extensions in XML importer.

* move ns relative functionality from parser to importer

* move rel ns handling to xml_import

* also move working version of _sort_nodes_by_parentid to xmlimport

* because moved methods updated test_unit.py

* theoretical fix and tests for namespaces xml exporter

* Revert "hack around broken namespace import from xml"

This reverts commit 1a5475f1.

* better testing av exporting and reimporting namespaces

add export import xml tests and fix et obj related bug

This reverts commit 3f750a92.