SOR Add hooks support

[johngrantuk]

• Any Balancer supported hook should be added to Balancer Maths package which will handle calculations given relevant pool and hook state.
• Any Balancer supported hook should also be added to API (by API team) which will handle collecting/storing relevant hook state.
• Pools with non-supported hooks should be ignored by SOR.
• In the current SOR implementation the BalancerMaths library is also being used with pool state provided from API. Hook state should be passed in a similar manner.
• Ideally we want to structure this in a way that makes this easy to do as we will likely have a number of hooks to support (doc of process would be helpful)

I'd suggest starting by adding support for the ExitFee hook. This has already been added to maths package and I believe Jarek has already added support in API.
See Balancer Maths ExitFee hook test for example of hook state required.
Currently maths uses hookType(see here) field on pool state to map a pool<>hook. Currently a string name. This may not match API implementation and we can figure out best approach.