WIP: Graph datahandling

This is the draft for a data handling that (optionally) forwards all calls to SerialDatahandling. All calls and data transfers get recorded for the creation of an execution graph.

Needs to be changed after the breaking changes in datahandling.

Needs a tiny change in lbmpy:

Instead of using TimeLoop(...) for time loop creation a custom function is used.

pystencils/opencl/opencljit.py

@@ -28,6 +28,20 @@ def init_globally(device_index=0):
     _global_cl_queue = cl.CommandQueue(_global_cl_ctx)
 
 
+def init_globally_with_context(opencl_ctx, opencl_queue):
+    global _global_cl_ctx
+    global _global_cl_queue
+    _global_cl_ctx = opencl_ctx
+    _global_cl_queue = opencl_queue
+
+
+def clear_global_ctx():
+    global _global_cl_ctx
+    global _global_cl_queue
+    _global_cl_ctx = None
+    _global_cl_queue = None
+
+
 def make_python_function(kernel_function_node, opencl_queue, opencl_ctx, argument_dict=None, custom_backend=None):
     """
     Creates a **OpenCL** kernel function from an abstract syntax tree which