Remove GModelPointSource, GModelExtendedSource and GModelDiffuseSource
Correct comment.
Make class non-abstract.

The GModelSky class is no longer abstract but is the general implementation of a sky model. For this purpose, the member m_type has been added that holds a string specifying the model type.

The type is now set automatically based on the type of the spatial component using the protected set_type() method.

More constructors have been added to allow building an object from the model components, including also the temporal component. Also, another constructor was added to allow using also temporal information from an XML element for construction.
The GModelSky class is no longer abstract but is the general implementation of a sky model.

The type is now set automatically based on the type of the spatial component using the protected set_type() method. The set_type() method is called by all non-void constructors and the XML read method.

The type provided in the XML file is for the moment ignored. The type will be set directly from the type of the spatial component.

More constructors have been added to allow building an object from the model components, including also the temporal component. Also, another constructor was added to allow using also temporal information from an XML element for construction.

Three instances of GModelSky are now registered using the types PointSource, ExtendedSource and DiffuseSource. This is only needed for correct interpretation of XML files.
Adapt to new GModelSky non-abstract class.
Remove casts to GModelPointSource, GModelExtendedSource and GModelDiffuseSource.

The GModelPointSource, GModelExtendedSource and GModelDiffuseSource classes have been removed and are now replaced by GModelSky.
Use GModelSky instead of GModelPointSource.

The GModelPointSource class has been removed. Now, GModelSky implements general sky models.
Remove unnecessary include file.
Use GModelSky instead of former model variants.
Print also model type.
Use GTime constructor instead of obsolete met() method.
Renamed.
Renamed from GModelSpatialPtsrc.i to GModelSpatialPointSource.i
Renamed from GModelSpatialPtsrc.cpp to GModelSpatialPointSource.cpp
Remove unnecessary include file.
Replace GModelSpatialPtsrc by GModelSpatialPointSource.
Remove GModelExtendedSource and GModelDiffuseSource includes.
Replace GModelSpatialPtsrc by GModelSpatialPointSource.
Remove unnecessary include file.
Replace GModelSpatialPtsrc by GModelSpatialPointSource.