Move XMLListModel to a standalone plugin to reduce the QtXmlPatterns dependancy

Investigate using 3rd party library as a replacement for QtXmlPatterns in XMLListModel

1. expat
http://expat.sf.net
Written in C, SAX, MIT Licensed, fast small and low memory usage.
No XPath feature

2. TinyXML & TinyXPath
http://www.grinninglizard.com/tinyxml/
http://tinyxpath.sourceforge.net/
zlib license
Not a full implementation
3. libxml2
http://xmlsoft.com
C, SAX and DOM, MIT Licensed
only support XPath 1.0 (QtXmlPatterns supports XPath 2.0)
Current XPath 2.0 support status:http://www.explain.com.au/libx/compliance.html

Benchmark report:
http://xmlbench.sf.net/results/benchmark200910/index.html