Modification in user groups

Now user groups are fixed as its ``` "_type": Author ```
Modification in : 
```
filldb.py  --> included code for already existing user document update for its "_type" as 'Author'
ndf_tags.py --> modification for fetching the user documents according to its _type 'Author'
ajax_views.py  --> user group query modified 
file.py  --> All groups including user groups query modified for user shelves
group.py  -->  All groups including user groups query modified for user shelves as well as for creating new groups
home.py  --> When user group creates when user logged in for first time , query modified according to "_type" as "Author"
methods.py  -->  In check_existing_group() function query modified according to its "_type"
page.py  --> user group query modified for shelves 
userDashboard.py  --> user group query modified for shelves
```
[NOTE: Please do "**python manage.py filldb**"  after latest pull ]