Combine storage traits and derives into single crate

[ascjones]

Follow up to #1331. Reviewers don't be alarmed this is just moving a bunch of stuff around.

This PR:

• Creates new ink_storage_traits crate
• Moves Storable definition and derive there (together with other traits)
• Moves some types to primitives to remove dependency on ink_env

It is to make life easier for storage derive macro crate identifiers in #1223.

• Currently ink_primitives contains the Storable trait definition and derive.
  • This is not a natural place for it, just required to avoid circular depenency (see below)
• ink_storage -> ink_env, so ink_env cannot depend on ink_storage (circular dependency)

[codecov-commenter]

Codecov Report

Merging #1389 (c0956e4) into master (c0956e4) will not change coverage.
The diff coverage is n/a.

❗ Current head c0956e4 differs from pull request most recent head 1dc778b. Consider uploading reports for the commit 1dc778b to get more accurate results

@@           Coverage Diff           @@
##           master    #1389   +/-   ##
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  Coverage   71.42%   71.42%           
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  Files         190      190           
  Lines        5873     5873           
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  Hits         4195     4195           
  Misses       1678     1678           

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[xgreenx]

It looks clearly now=)
I like that Storable in the right place right now. And I definitely like definition of the AccountId, Hash in the ink_ptimitives=)