Fixed #129. task assigned autocomplete ui bug.

Append a patch.css to fix this.

I found there are many css files not included in treeio's source tree. There is only 26a.min.css but no source or instructions about how to build it. I guess the most important treeio3.css was built from static/styles/tree.less but I found that seems not synced (there is `.popup-block .ui-autocomplete` setting in it but not appeared in 26a.min.css). 

So I decided not to touch these files, just add a patch.css to fix this problem.