User leaves outline item editing, node content should be checked for URLs

[electronicbites]

trafficstars

• [] If content contains an URL it should be made visible to the user via an indicator (e.g. automatic link)
• [] Unfurling should be initiated in an async task
• [] Command and Event should to be defined
• [] The result of the unfurling should be persisted (in a new table)

The implementation should be as simple as possible. More complex scenarios need an extra ticket