refactor nodes into standalone file

backend/nodes/__init__.py

@@ -1,7 +1,54 @@
 # Import all node modules to trigger @register_node decorators.
-from . import io, filters, modify, level, analysis, mask, display
+from backend.nodes import (
+    # IO
+    image,
+    image_demo,
+    folder,
+    coordinate,
+    coordinate_pair,
+    number,
+    range_slider,
+    save_image,
+    # Filters
+    gaussian_filter,
+    median_filter,
+    edge_detect,
+    fft_filter_1d,
+    fft_filter_2d,
+    # Modify
+    colormap_adjust,
+    crop_resize_field,
+    rotate_field,
+    # Level
+    plane_level_field,
+    poly_level_field,
+    fix_zero,
+    # Mask
+    draw_mask,
+    threshold_mask,
+    mask_morphology,
+    mask_invert,
+    mask_combine,
+    # Display
+    color_map,
+    font_node,
+    annotations,
+    markup,
+    preview_image,
+    view_3d,
+    print_table,
+    value_display,
+    # Analysis
+    statistics_node,
+    histogram,
+    cursors,
+    fft_2d,
+    inverse_fft_2d,
+    cross_section,
+    stats,
+)
 
 try:
-    from . import particle
+    from backend.nodes import particle_analysis
 except ImportError:
-    from . import particless
+    pass