iOS/Bookmarks

[SRihet]

Description

Implements the Bookmarks Store and adds bookmarks buttons to the agenda cells and session details.

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [] Enhancement (non-breaking change which cleans up / improves existing functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)