T45687: Rework the Export/Import of Animations

This started with a fix for an animated Object Hierarchy. Then i decided to cleanup and optimize a bit. But at the end this has become a more or less full rewrite of the Animation Exporter. All of this happened in a separate local branch and i have retained all my local commits to better see what i have done.

Brief description:

* I fixed a few issues with exporting keyframed animations of object hierarchies where the objects have parent inverse matrices which differ from the Identity matrix.
* I added the option to export sampled animations with a user defined sampling rate (new user interface option)
* I briefly tested Object Animations and Rig Animations.

What is still needed:

* Cleanup the code
* Optimize the user interface
* Do the Documentation

Reviewers: mont29

Reviewed By: mont29

Differential Revision: https://developer.blender.org/D3070

source/blender/collada/collada_utils.cpp

@@ -53,6 +53,7 @@ extern "C" {
 #include "BKE_mesh.h"
 #include "BKE_scene.h"
 #include "BKE_DerivedMesh.h"
+#include "BKE_main.h"
 
 #include "ED_armature.h"
 
@@ -132,6 +133,17 @@ int bc_set_parent(Object *ob, Object *par, bContext *C, bool is_parent_space)
 	return true;
 }
 
+Main *bc_get_main()
+{
+	return G.main;
+}
+
+EvaluationContext *bc_get_evaluation_context()
+{
+	Main *bmain = G.main;
+	return bmain->eval_ctx;
+}
+
 Object *bc_add_object(Scene *scene, int type, const char *name)
 {
 	Object *ob = BKE_object_add_only_object(G.main, type, name);