sanitise an edited asset before saving
When saving an asset, sanitise the fields before saving. Specifically:
- if the asset does not contain personal data, clear the personal fields.
- if the asset is not shared outside the University, clear the description of who it is shared with.
- if the asset is not shared outside the EEA, clear the description of who it is shared with.
- if the asset is not digital, clear the digital security measures.
- if the asset is not physical, clear the physical security measures.
- if the asset does not have purpose: "other", clear the purpose_other field
- if the asset does not have purpose: "research", clear the owner field.
Closes #64 (closed)