Make it easier to use with fewer transactions

[xrchz]

Do we want to rely on multicall, or should we have more batch functions that take e.g. multiple pool ids?

Also: combine withdrawEtherFromPool and withdrawFromPool into one.

[xrchz]

Disadvantage of multicall: some checks happen multiple times, like auth checks.
Diasdvantage of dedicated batching: need to implement more contract code, functions could get more complicated.
Probably we should focus on reducing transactions for common cases and consolidating functions where they become simpler, but without developing a whole batch language or policy.

[xrchz]

On the borrower side we could consolidate minipool refunds and distributes probably (similar to how it is for lenders)