[feat] promote experience about floor creation.

- change bl_options and rewrite invoke and draw functions to let floor creating window become more visual. credit: BLumia.
- also change 3ds max align and flatten uv presentation after changing creating floor window.
- seperate icon loader/unload module.

ballance_blender_plugin/UTILS_icons_manager.py

@@ -0,0 +1,30 @@
+import bpy
+import bpy.utils.previews
+import os
+from . import UTILS_constants
+
+# ImagePreviewCollection ccreated by Blender
+floor_icons = None
+# a map. key is block name, value is loaded icon id
+floor_icons_map: dict = {}
+
+def register_icons():
+    global floor_icons, floor_icons_map
+
+    icon_path = os.path.join(os.path.dirname(__file__), "icons")
+    floor_icons = bpy.utils.previews.new()
+    for key, value in UTILS_constants.floor_blockDict.items():
+        blockIconName = "Ballance_FloorIcon_" + key
+        floor_icons.load(blockIconName, os.path.join(icon_path, "floor", value["BindingDisplayTexture"]), 'IMAGE')
+        floor_icons_map[key] = floor_icons[blockIconName].icon_id
+
+def unregister_icons():
+    global floor_icons, floor_icons_map
+
+    bpy.utils.previews.remove(floor_icons)
+    floor_icons_map.clear()
+
+def get_floor_icon(floor_blk_name: str):
+    global floor_icons_map
+
+    return floor_icons_map[floor_blk_name]