Tag improvements

[geoversed]

• Allow for tags to be available and stored on a per-user basis
• Allow for tags to be available and stored on a per-guild basis
• Toggle visibility status for a tag (between public and private)
• Add different types of tags such as system tags which are owned by the bot which provide explanations/guides/tutorials for using it. Can be a way to resolve Better the beginner experience #141

For the last task, another non-inline embed field can be added in the tag information command to add further details about the tag itself.