Notification Sub-system

[cnangeh]

Work done:

• Work done by Adhyan last year
• User subscription to topic on user creation
• Topic creation on entity creation
• Upgrade process of user notification
• Migration script - topic, topic subscription models for new and already existing users and entities
• Update user subscription on user transfer and/or update of user's permission
• Update topic details when entity details updates
• Update topic details when member type are updated at the system level
• Unit test topic-subscriber model

[nazeer1100126]

@Anh3h please send PR after rebasing to latest code. Your PR shouldn't have Adhyan changes

[cnangeh]

Ok. I will do that

[cnangeh]

@nazeer1100126 Here is the updated pull request: #405