Use prefix store for contract history

[alpe]

Resolves #196
After #199

Includes new CLI command:
wasmcli query wasm contract-history [bech32_address] to print all the code changes.

wasmcli q wasm contract-history cosmos18r5szma8hm93pvx6lwpjwyxruw27e0k5uw835c
[
  {
    "operation": "Init",
    "code_id": 1
  },
  {
    "operation": "Migrate",
    "code_id": 2
  }
]

Note: to be on the safe side sequences have their own prefix as well.

This PR also updates the codec to fix the message decoding issue.

---

For admin use:

• Added appropriate labels to PR (ex. WIP, R4R, docs, etc)
• Reviewers assigned
• Squashed all commits, uses message "Merge pull request #XYZ: [title]" (coding standards)

[codecov]

Codecov Report

Merging #208 into master will increase coverage by 0.07%.
The diff coverage is 55.40%.

@@            Coverage Diff             @@
##           master     #208      +/-   ##
==========================================
+ Coverage   71.87%   71.95%   +0.07%     
==========================================
  Files          27       27              
  Lines        2610     2624      +14     
==========================================
+ Hits         1876     1888      +12     
+ Misses        624      623       -1     
- Partials      110      113       +3     

Impacted Files	Coverage Δ
x/wasm/internal/keeper/genesis.go	96.55% <ø> (-0.06%)	⬇️
x/wasm/internal/keeper/test_fuzz.go	94.59% <ø> (-0.53%)	⬇️
x/wasm/internal/types/genesis.go	94.73% <ø> (-0.27%)	⬇️
x/wasm/internal/types/keys.go	0.00% <ø> (ø)
x/wasm/internal/types/test_fixtures.go	93.86% <ø> (-0.04%)	⬇️
x/wasm/internal/types/types.go	23.68% <0.00%> (+0.80%)	⬆️
x/wasm/internal/keeper/querier.go	41.35% <56.52%> (+2.51%)	⬆️
x/wasm/internal/keeper/keeper.go	91.00% <100.00%> (-0.21%)	⬇️
x/wasm/internal/types/codec.go	100.00% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 1c4d4d8...ad520ed. Read the comment docs.

[ethanfrey]

Looks good to merge.

Can you please add a migration guide for the client-visible changes (on queries)? So they can update CosmJS easier

[alpe]

Pushed a fix for the history query response together with a api_migration.md file

[ethanfrey]

Thank you for adding this.

There is also a code -> code_id renaming from another PR I believe

[alpe]

It was code_id in the json before. Only the Go code was inconsistent. There are no changes for the clients