Map rendering based on user's last edited marker and Tag Browser work initiated.

**Please run : ```python manage.py filldb```** command after getting this pull request.

Showing map view based on user's last edited marker : 
 - When user is logged in then his/her latest visited/edited/created marker's map view will be stored. This is stored in ```Author``` class.
 - New field ```'visited_location': []``` added into Author class of models.py
 - When user is not logged in then marker view else default view will be shown.

Tag Browser work initiated : 
 - New template ```tag_browser``` is added.