Integrated DE plugin functionality.
Reworked DE components:
- TKDESTEP: Handling STEP file format.
- TKDEOBJ: Handling OBJ file format.
- TKDEIGES: Handling IGES file format.
- TKDEGLTF: Handling GLTF file format.
- TKDEVRML: Handling VRML file format.
- TKDEPLY: Handling PLY file format.
- TKDESTL: Handling STL file format.
Reworked DE DRAW components:
TKXSDRAWSTEP: Container for DE command to work with STEP.
TKXSDRAWOBJ: Container for DE command to work with OBJ.
TKXSDRAWIGES: Container for DE command to work with IGES.
TKXSDRAWGLTF: Container for DE command to work with GLTF.
TKXSDRAWVRML: Container for DE command to work with VRML.
TKXSDRAWPLY: Container for DE command to work with PLY.
TKXSDRAWSTL: Container for DE command to work with STL.
TKXSDRAW rework to be base DRAW plugin to keep DE session and utils.
Updated documentation
Updated samples
Added Qt sample OCCTOverview providing examples of use of OCCT API with relevant code and demonstration of results in the viewer.
Off-topic: some unused images are removed from dox/introduction/images/
