Add lastAccessed field to map table

[JannikStreek]

Proposed feature
We would like to standardize our deletion policies of old data across our open source apps. To make it as easy as possible, we have decided to leverage the last access of a created entity. Currently teammapper does not have such a field on the map entity and we use the lastModified field.

• Add a lastAccessed timestamp field to map entity
• The field should get updated when findOne is called in the controller => Please check that this method is actually called when accessing a map, I think it should be called.
• Adapt the deletion algorithm in the map service to use this field instead of lastModified and as a backup the old field should be used (as many legacy maps don't have any data inside the new field).