Changed xsd url paths and combined two xml writer / reader tests.

Xsd are searched for on the opengeosys.org website. This fixes the
60 seconds xml reader timeout bug.

The two tests are combined because there execution order is important
which is not guaranteed in gtest.
Removed mandatory reference to a XML schema file in XML-IO classes.

These references are now hardcoded in the class constructors of the
XML-IO classes. Also the definition of the two search paths in
BaseLib::FileFinder from the main window are now moved into the
constructor of FileFinder.

XML schema files are first searched (for validation) by their path
and then by the reference in the XML file itself.
Fixed utils.
Removed file finder mainwindow variable.
Merge pull request #258 from bilke/xsd-paths

Fix the xml timeout bug!