Introduce Claim and Credential stores per context

[silvin-lubecki]

- What I did The new application store persists everything inside the docker config directory. It initializes 3 stores

• bundle store, common between contexts
• claim stores, one per context
• credential stores, one per context

- How to verify it

We can now re-use the same name on different contexts:

$ docker app install examples/hello-world/hello-world.dockerapp --name=hello --target-context=swarm
...
$ docker app install examples/hello-world/hello-world.dockerapp --name=hello --target-context=kubernetes
...
$ docker app install examples/hello-world/hello-world.dockerapp --name=hello --target-context=swarm
Error: installation "hello-world" already exists

- Description for the changelog

• Add an Application Store, which can initialize a common bundle store, a claim store per context and a credential store per context.
• Removed duffle home dependency

- A picture of a cute animal (not mandatory but encouraged)

[silvin-lubecki]

PTAL @simonferquel

[silvin-lubecki]

Fixed all your comments @simonferquel, and also renamed claim store to installation store. PTAL

[codecov[bot]]

Codecov Report

Merging #507 into master will decrease coverage by 0.37%. The diff coverage is 63.75%.

@@            Coverage Diff             @@
##           master     #507      +/-   ##
==========================================
- Coverage   69.56%   69.19%   -0.38%     
==========================================
  Files          51       53       +2     
  Lines        2744     2818      +74     
==========================================
+ Hits         1909     1950      +41     
- Misses        592      607      +15     
- Partials      243      261      +18

Impacted Files	Coverage Δ
internal/commands/pull.go	69.23% <42.85%> (-10.77%)	:arrow_down:
internal/commands/install.go	62.5% <50%> (-2.58%)	:arrow_down:
internal/commands/root.go	88.05% <52.94%> (-11.95%)	:arrow_down:
internal/commands/upgrade.go	60.37% <57.14%> (-3.09%)	:arrow_down:
internal/commands/uninstall.go	61.53% <60%> (-4.26%)	:arrow_down:
internal/store/credential.go	63.63% <63.63%> (ø)
internal/commands/cnab.go	69.72% <64.28%> (-0.77%)	:arrow_down:
internal/store/bundle.go	68.88% <68.88%> (ø)
internal/commands/status.go	60.97% <71.42%> (-4.03%)	:arrow_down:
internal/store/app.go	73.33% <73.33%> (ø)
... and 4 more

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