new:
1.add button in GUI to delete friend, click on user head img to activate;
2.add join group apply msg handle and confirm msg in message center;
3.add join_group_apply and join_group_confirm procedure in message.handles.py

modification:
1.re-struct the code in group views.py PUT view, logic more clear now.
2.some fix of javascript code in index.js
Merge branch 'master' of github.com:AllChat/AllChat