`create_kernel` API Update

To reduce the kwargs hell, we introduced dataclasses, which handle the settings of create_kernel and similar functions. In addition we introduced type-hints for the API functions to increase usability and simplify development.

pystencils/datahandling/__init__.py

+import warnings
+
 from typing import Tuple, Union
 
 from .datahandling_interface import DataHandling
@@ -34,6 +36,12 @@ def create_data_handling(domain_size: Tuple[int, ...],
         parallel: if True a parallel domain is created using walberla - each MPI process gets a part of the domain
         default_ghost_layers: default number of ghost layers if not overwritten in 'add_array'
     """
+    if isinstance(default_target, str):
+        new_target = Target[default_target.upper()]
+        warnings.warn(f'Target "{default_target}" as str is deprecated. Use {new_target} instead',
+                      category=DeprecationWarning)
+        default_target = new_target
+
     if parallel:
         assert not opencl_queue, "OpenCL is only supported for SerialDataHandling"
         if wlb is None: