Refactor for v0.4

Major refactoring!

• Uses lazy loading for imports
• Utils is set for internal tools only

qim3d/cli.py

 import argparse
 import webbrowser
 import outputformat as ouf
-import qim3d.io
-from qim3d.viz.preview import image_preview
-from qim3d import __version__ as version
+import qim3d
 
 QIM_TITLE = ouf.rainbow(
-    f"\n         _          _____     __ \n  ____ _(_)___ ___ |__  /____/ / \n / __ `/ / __ `__ \ /_ </ __  /  \n/ /_/ / / / / / / /__/ / /_/ /   \n\__, /_/_/ /_/ /_/____/\__,_/    \n  /_/                 v{version}\n\n",
+    f"\n         _          _____     __ \n  ____ _(_)___ ___ |__  /____/ / \n / __ `/ / __ `__ \ /_ </ __  /  \n/ /_/ / / / / / / /__/ / /_/ /   \n\__, /_/_/ /_/ /_/____/\__,_/    \n  /_/                 v{qim3d.__version__}\n\n",
     return_str=True,
     cmap="hot",
 )
@@ -42,9 +40,9 @@ def main():
         "--no-browser", action="store_true", help="Do not launch browser."
     )
 
-    # K3D
+    # Viz
     viz_parser = subparsers.add_parser("viz", help="Volumetric visualization.")
-    viz_parser.add_argument("--source", default=False, help="Path to the image file")
+    viz_parser.add_argument("filename", default=False, help="Path to the image file")
     viz_parser.add_argument(
         "--destination", default="k3d.html", help="Path to save html file."
     )
@@ -116,20 +114,20 @@ def main():
     args = parser.parse_args()
 
     if args.subcommand == "gui":
-        from qim3d.gui import annotation_tool, data_explorer, iso3d, local_thickness
+        import qim3d.gui
 
         arghost = args.host
         inbrowser = not args.no_browser  # Should automatically open in browser
 
         interface = None
         if args.data_explorer:
-            interface_class = data_explorer.Interface
+            interface_class = qim3d.gui.data_explorer.Interface
         elif args.iso3d:
-            interface_class = iso3d.Interface
+            interface_class = qim3d.gui.iso3d.Interface
         elif args.annotation_tool:
-            interface_class = annotation_tool.Interface
+            interface_class = qim3d.gui.annotation_tool.Interface
         elif args.local_thickness:
-            interface_class = local_thickness.Interface
+            interface_class = qim3d.gui.local_thickness.Interface
         else:
             print(
                 "Please select a tool by choosing one of the following flags:\n\t--data-explorer\n\t--iso3d\n\t--annotation-tool\n\t--local-thickness"
@@ -145,12 +143,12 @@ def main():
             interface.launch(inbrowser=inbrowser, force_light_mode=False)
 
     elif args.subcommand == "viz":
-        if not args.source:
-            print("Please specify a source file using the argument --source")
-            return
+        import qim3d.viz
+        import qim3d.io
+
         # Load the data
-        print(f"Loading data from {args.source}")
-        volume = qim3d.io.load(str(args.source))
+        print(f"Loading data from {args.filename}")
+        volume = qim3d.io.load(str(args.filename))
         print(f"Done, volume shape: {volume.shape}")
 
         # Make k3d plot
@@ -163,9 +161,12 @@ def main():
             webbrowser.open_new_tab(args.destination)
 
     elif args.subcommand == "preview":
+        import qim3d.viz
+        import qim3d.io
+
         image = qim3d.io.load(args.filename)
 
-        image_preview(
+        qim3d.viz.image_preview(
             image,
             image_width=args.resolution,
             axis=args.axis,
@@ -174,6 +175,8 @@ def main():
         )
 
     elif args.subcommand == "convert":
+        import qim3d.io
+
         qim3d.io.convert(args.input_path, args.output_path, chunk_shape=args.chunks)
 
     elif args.subcommand is None:
@@ -188,9 +191,6 @@ def main():
         parser.print_help()
         print("\n")
 
-    elif args.subcommand == "convert":
-        qim3d.io.convert(args.input_path, args.output_path)
-
 
 if __name__ == "__main__":
     main()