Implement the "CommunityPoolSpendProposal" as described in Cosmos Hub proposal 7.
Also a useful test of Git flow for merging features passed in governance proposals.
Gaia is removed from cosmos-sdk repository.
Few changes were required to make sure no packages depend on gaia subpackages.
CI config is amended accordingly.
Unnecessary targets are removed from Makefile.
Simulations run through a lightweight version of gaia renamed to simapp.
Closes: #4104
* add a bunch of tests, add DONTCOVER text tag
- Also fix flaky test (closes: #3559). Don't test values
returned by queries since there's no way to query a
specific height via REST.
* GetTempDir -> NewTestCaseDir
* Move query and tx commands to modules
* Move GetAccountDecoder to prevent import cycle and replace calls to it with one call in WithAccountDecoder
* Add moduleClients interface and implement in all applicable modules
* Use module clients in cli initialization
