Start restructuring of app to make it more modular, and improve layout a bit

app/components/instrument_dashboard.py

@@ -0,0 +1,36 @@
+
+from dash import Dash, html, dcc, callback, Output, Input, State, dash_table
+import dash_bootstrap_components as dbc
+
+instrument_dashboard = dbc.Row([
+    html.H3("Select data table"),
+        
+    # First Dropdown (Instrument Folders)
+    dcc.Dropdown(
+        id="instrument-dropdown",
+        options=[{"label": i, "value": i} for i in []],
+        placeholder="Select an Instrument Folder",
+    ),
+
+    # Spinner wrapping the second and third dropdowns
+    dcc.Loading(
+        type="circle",  # Spinner style
+        children=[
+            # Second Dropdown (Files)
+            dcc.Dropdown(
+                id="file-dropdown",
+                placeholder="Select a File",
+                disabled=True  # Initially disabled
+            ),
+            
+            # Third Dropdown (Sub-selection)
+            dcc.Dropdown(
+                id="sub-dropdown",
+                placeholder="Select Variables",
+                multi = True,
+                disabled=True
+            )
+        ]
+    )
+    ], 
+    justify="center", align="center",style={'background-color': '#f8f9fa', 'padding': '20px', 'text-align': 'center'})