gometalinter -> golangci-lint migration (#3933)

{,scripts/}Makefile:
- Remove gometalinter, install golangci-lint.
- Remove distinction between tools and devtools.
  Just tools is enough.
- test_lint -> lint
  Migrating away from underscore separated names.
- Remove unnecessary targets.
- Drop tendermint/lint. Incompatbile with golangci-lint
  and no longer necessary anyway.
- Fix misleading message in go-mod-cache.
- New ci-target to avoid download tools twice.
- Run tests with -mod=readonly.

Port tools/gometalinter.json to .golangci.yml
Update CircleCI config accordingly.

Closes: #3896

client/tx/broadcast.go

@@ -110,7 +110,7 @@ $ gaiacli tx broadcast ./mytxn.json
 			}
 
 			res, err := cliCtx.BroadcastTx(txBytes)
-			cliCtx.PrintOutput(res)
+			cliCtx.PrintOutput(res) // nolint:errcheck
 			return err
 		},
 	}

client/tx/encode.go

@@ -97,7 +97,7 @@ If you supply a dash (-) argument in place of an input filename, the command rea
 			txBytesBase64 := base64.StdEncoding.EncodeToString(txBytes)
 
 			response := txEncodeRespStr(txBytesBase64)
-			cliCtx.PrintOutput(response)
+			cliCtx.PrintOutput(response) // nolint:errcheck
 
 			return nil
 		},