Explicitely declare inline methods.
Make sure that scale is never zero.
Add GModelPar test cases.
name() method returns const reference.
Merge branch 'integration' into 773-review-model-classes
Declare methods inline.

The methods that are implemented in the header file are now explicitely declared inline and put in a dedicated section after the class declaration. This enables proper documentation of the methods.

A small semantic bug was also fixed in the reserve() method where the reserve class was put after return. This apparently worked, but is not correct as the method returns void.
Declare methods inline and improve documentation.
Add GModelSky unit tests.
Declare methods inline, improve documentation.
Add value constructor and access methods, implement mc method, declare inline methods.
Add GModelSpatialDiffuseConst unit test.
Add XML test file.
Clear model before reading.
Add value constructors and access methods.
Add GModelSpatialDiffuseCube unit tests.
Rename from *_spatial_* to *_diffuse_*
Add model evaluation call graph.
value and gradients methods now take GPhoton as argument
Add map cube test file
Add missing parameters for Doxygen documentation.