Read-Unread System and indicators

[Boss-1s]

indicators will lead to advanced layering and clone limits....
may have to use pen engine for text

currently notifications are planned to be stored locally (due to privacy concerns)

still thinking of:

• should notifications be stored using key_multivalue_storage here or just on the project (locally)?
• should a notification be deleted after a set amount of time when marked as read?
• should clones be used or sprites for the system's ui?