Feat/repay withdraw all gas cost

[Rubilmax]

The gas cost of a withdrawAll in this case is:

In other words, it saves almost 3k gas (~4%) to have a withdrawAll mechanism inside Blue

Note that the benefit of #183 is that amount needs to be calculated upfront by the integrator, which allows them to also have access to it afterwards. To have similar usecases, I use balanceOf to calculate the amount actually withdrawn. Gas savings can be up to 4.5k if a return value is added to withdraw, just like in #181 (gas diff showcased in #185).