Include admin support to {exp_data|overlay}_uri (#45)
Override uploaded file when field_uri is provided (#45 note-9)
[slices] Differenciate exp_data and overlay set methods (#45 note-13)

a) upload a file (sha256 is automatically generated)
b) set URI and SHA256 together.
[slices] Allow overriding _uri via API when exists a uploaded file (#45 note-14)
Merge branch 'feature45' (#45)