Refactor packaging

Hi all,

This MR aims to improve the packaging of the toolbox. In general, deleting globals tend to have unwanted consequences. For instance, I have encountered import problems during unit testing. The refactoring has a similar outcome as the previous implementation, which is clean namespace. This is due to the __all__ being listed to each modules, as suggested here.

I also have listed all the required libraries for the Toolbox. One can now freely install the library on a local environment with pip install -e ".[maxwell]". The maxwell tag is a side effect of a direction that I would like to suggest. That is, the Toolbox codes can be used elsewhere; maybe in conjunction with another library, maybe as a Karabo device.

Please feel free to let me know your thoughts :)

@lleguy @mercurio @mercadil @teichman

src/toolbox_scs/routines/__init__.py

-from .XAS import (
-    xas, xasxmcd)
-from .knife_edge import knife_edge
+from .XAS import *
+
+# Module name is the same as a child function, we use alias to avoid conflict
+import toolbox_scs.routines.knife_edge as knife_edge_module
+from .knife_edge import *
 
 __all__ = (
-    # Functions
-    "xas",
-    "xasxmcd",
-    "knife_edge"
+    knife_edge_module.__all__
+    + XAS.__all__
 )
-
-# -----------------------------------------------------------------------------
-# Clean namespace
-#     -> certain filenames we dont need in the namespace. Especially not those
-#     that are marked as private by using an underscore (_<filename>.py).
-# -----------------------------------------------------------------------------
-
-clean_ns = [
-    # filenames
-    'XAS',
-    ]
-
-
-for name in dir():
-    if name in clean_ns:
-        del globals()[name]
-
-del globals()['clean_ns']
-del globals()['name']