* add message types for swaps
* add tx client commands
* add test coverage for swap message deadlines
* start handler swap tests, export handler result message event into
private method, add stubbed keeper methods
* add initial swap implementation to get handler tests passing; adds event
specific for trades
* add handler acceptance test for slippage in exact input and exact output
swaps
* implement slippage limit for swap keeper methods
* add tests to ensure a user can only swap spendable coins
* test pool not found, panic on invalid pool, and panic when module
account does not have enough funds
* validate that the exact output when using for exact swaps is less than
the pool liquidity
* nit: long line
* add validation that swap output is greater than zero
* add rest txs for swap messages
* nit: lints
* dry up swap keeper methods
* from pr feedback - spelling and increase clairty around the output
amount of a swap rounding to zero
