Don't show ID as repository in image ls

[zappy-shu]

- What I did

When running image ls images without a repository no longer print
their ID as their repository.

- How I did it

If the image isn't a reference.Named then print <none> instead of the FamiliarString for the REPOSITORY column

- How to verify it

Pull an image from hub by digest and then run app image ls --digest. The image in question should show the digest prefixed by the algorithm type. E.g.

REPOSITORY   TAG    DIGEST          APP IMAGE ID APP NAME
<none>       <none> sha256:<digest> <id>         <name>

- Description for the changelog

image ls prints <none> in as the repository when the image does not have a tag

- A picture of a cute animal (not mandatory)

[codecov]

Codecov Report

Merging #728 into master will increase coverage by 0.56%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master    #728      +/-   ##
=========================================
+ Coverage   70.94%   71.5%   +0.56%     
=========================================
  Files          61      60       -1     
  Lines        3493    3201     -292     
=========================================
- Hits         2478    2289     -189     
+ Misses        695     604      -91     
+ Partials      320     308      -12

Impacted Files	Coverage Δ
internal/commands/image/list.go	83.67% <100%> (ø)	⬆️
internal/packager/init.go	61.68% <0%> (-9.13%)	⬇️
internal/commands/root.go	73.86% <0%> (-4.65%)	⬇️
internal/packager/cnab.go	97.91% <0%> (-0.09%)	⬇️
internal/names.go	100% <0%> (ø)	⬆️
internal/commands/inspect.go
internal/inspect/inspect.go	86.88% <0%> (+8.09%)	⬆️

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