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/datahandling/serial_datahandling.py

@@ -272,6 +272,8 @@ class SerialDataHandling(DataHandling):
     def synchronization_function(self, names, stencil=None, target=None, **_):
         if target is None:
             target = self.default_target
+        if target == 'opencl':
+            target = 'gpu'
         assert target in ('cpu', 'gpu')
         if not hasattr(names, '__len__') or type(names) is str:
             names = [names]