Using std::string instead of QString for file name.

Wrapps readFile(QString).
Removed definition of 'int XmlGmlInterface::readFile(std::string const&)'.
Changed signature of virtual Writer::write().
[BoostXmlCndInterface] Made reading/parsing of geometry tag xml more clear.
Added CondType _type to decide what type of condition should be written.
Added some code for writing conditions to xml file.