added angle-parameter to extract surfaces more precisely
formatting
find x
changes based on PR comments
removed binary file and fixed intentation
exchanged pi-constant for radian-constant
added doxygen filename tags
Reduce indentation by reordering if clause.
Use std::size_t instead of size_t.
getSurfaceAreaForNodes() returns its result.

Also correct a description.
manually added changes by @endJunction that couldn't be added due to merge conflicts
replaced boost::radian with boost::pi again because the former didn't give the desired result
transferred OGSFileConverter-files from OGS5 to OGS6 and adjusted everything as needed
adjusted cmake files
fixed logog-problem and optimised code a little
added license information
First OGS simulation main program.
[A] Remove QtXml dependency and linking to qt/vtk.
[A] Include copyright and version info.
[A] Make project file argument unlabeled.

This is not an optional argument and the extra flag is not necessary.
Specify arguments help info.