Tracking all the activities of the user.

LogEntryManager of django admin is used here.
log_action method takes time, user, objects, action type and message as
its arguments.
For every action, the log_action is called. So that each user activity
is logged.
The logging can be further modified as per our requirement
Model added for activity log. Model is inheriting admins log model

All the activities for a given proposal is available for the reviewer.
Merge pull request #2 from prathamesh920/log_activities

Tracking all the activities of the user.