fix issue. add feat.

- add ignored bmesh update function in flatten uv
- finish select by group, add, rm, clear group functions.

.gitattributes

@@ -2,5 +2,6 @@
 *.png binary
 # our generated mesh should be save as binary
 *.bin binary
-# the compressed json data should be binary
+# the raw json data should be binary
+# although i edit it manually
 bbp_ng/raw_jsons/*.json    binary