Add slippage param when supplying liquidity

[hetfly]

[FezBox]

@hetfly is this still a valid issue?

[hetfly]

@FezBox yes, but not a priority imo. There was a new feature added while providing liquidity to protect users. Now it defaults to 2%, in the future we could add an UI input to edit the default slippage.

[FezBox]

when providing liquidity we want t he user to be able to specify maximum slippage

[parrot9design]

Here's how I thought we could handle this:

(Makes it easy to add in the transfer fee(s) once we take this cross-chain)

The slippage tooltip should say:

If the price slips by more than this, your liquidity transaction will fail.