Upgrade Cosmos SDK to v0.37.15

[youngjoon-lee]

Closes #53

Changes

There are so many breaking changes when upgrading medibloc/cosmos-sdk from v0.34.7 to v0.37.15.

1. Most of boilerplate codes were moved into the cosmos-sdk. So, many Go packages were removed from the panacea-core.

   app/genesis.go
   app/invariants.go
   init/{collect.go, genesis_accts.go, gentx.go, ...}
   server/
   types/assets/
   version/
   

   • It also caused many changes in the app/app.go and cmd/**/main.go, but most of them are straight-forward fortunately.
   • Especially, the custom parameter definitions in the app/genesis.go were moved to the medibloc/cosmos-sdk repo. Please see Modify default genesis params for Panacea cosmos-sdk#3.

2. The x/**/module.go was added.

   • For the latest cosmos-sdk, each module (x/) must implement AppModuleBasic and AppModule, so that they can be managed by ModuleManager. (link)

3. The x/**/keeper.go and some keeper-related codes were moved into the x/**/keeper/, according to the new recommended directory structure.

4. The genesis-related types were moved into the x/**/types/, according to the new recommended directory structure.

Tests

• Unit tests
• Running panacead from scratch
• AOL/DID operations

[cl9200]

👍

[youngjoon-lee]

I also tested all commands in our manual. All works well. I'd say this PR is safe to be merged.