Notifications: Improve layout and content for different use cases

[AntonLV]

• 1. Remove 'UNA Notification' prefix from email notifications and check Push notifications for the same behaviour.
• 2. Content module should be able to provide a setting which will control the way of how a notification will be shown (separate page, popup, etc)
• 3. Notification about comment in timeline update link to Update and highlight the comment.
• 4. Filter out unnecessary data for API calls responses and conver HTML special chars.

[makeplane]

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UNA-97 Notifications: Improve layout and content for different use cases