Don't reduce stake while adding liquidity

[reubenr0d]

Currently stake is reduced while adding liquidity, in the token.transfer handler. However if the transfer is due to adding liquidity then the stake is still held by the LP provider, so it shouldn't be reduced.

In that case same while removing liquidity, stake should not be added.

[reubenr0d]

In order to achieve this in the event handlers for adding/removing liquidity we add/subtract from the stake, such that the effects of stake on transfer are neutralised.

TODO: What when users transfer LP Tokens? Should stake get transferred to that user then?