[fix] fix add floor alignment and add some new icons.

- try setting center alignment for add floor popup operator. it is not center alignment now because blender's impl but it is better than previous layout.
- add some components icon for more directly visual.

.gitattributes

@@ -1,3 +1,5 @@
+# all png are binary
+*.png binary
 # our generated mesh should be save as binary
 *.bin binary
 # json is data and not good for human reading(althought I edit it on my own hand.)