Update for changed interface of boost >= 1.55.

The boost::property_tree::xml_writer_settings interface changed from Char type to String type. A preprocessor if for boost version <= 1.55 added to include old versions.
Merge pull request #459 from endJunction/Boost156XmlWriterUpdate

Update for changed interface of boost >= 1.55.
Remove/Comment ProjectData related changes.

The ProcessInfo and the boundary conditions are changing.
The FEMCondition's are depricated.

We change to variable-centred initial and boundary
conditions.
Remove FEMCondition and its BoostXml reader.
Remove ProcessInfo class as well.
Implementation of IC/BC and ProcessVariable.
Empty GroundwaterFlowProcess and its Base classes.
[PL] Add ProcessLib to CMake files.
Add ProcessLib to doxygen inputs.
[PL] Add virtual initialize().
[PL] Add number of node variables.

Element variables are not yet used.
[PL] Add destructor for GroundwaterFlowProcess.
Adjusted GUI for removed FEMCondition classes
In gui also comment out unused addCNDAction.
[PL] Include class Process into ProjectData.
[Tests] Removed TestBoostXmlCndInterface.

The test tested class BoostXmlCndInterface, that is removed previously.
[CLI] Vector for storing ProcessVariables.
[ProjectData] Make attribute name readable/consistent.
[ProjectData] Add configuration of project to ProjectData.
[ProjectData] Path argument for ProjectData constructor.