fix(gov): cli command for params and upgrade proposals

[tbruyelle]

Description

Closes: #39

The fix just copies the 3 command handlers for

• params.ParamChangeProposal
• upgrade.SoftwareUpgradeProposal
• upgrade.CancelSoftwareUpgradeProposal and replace the MsgSubmitProposal package with the one from govgen.

As a result WrapPropposalHandler is becomes obsolete, we only need to wrap the ProposalRESTHandler.

The fix has been tested with the json-signer test framework, see https://github.com/tbruyelle/json-signer/blob/master/testdata/govgenV1/gov-submit.txtar#L13-L50

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