refactor XCM emulator

[xlc]

Currently XCM emulator makes too much assumption about everything so that it is not generic and cannot be used for many commonly enough setups such as non u128 balance type or H160 account id type.

A large refactor is required to remove those assumptions and move all the code depends on pallet-balances to a separate optional extension. Not every chain have pallet-balances. Each chain may have different AccountId type and Balance type and they have to be configurable.

[NachoPal]

@xlc Please take a look at #2958

Hopefully you'll see some of the improvements you were asking (removed Balance pallet dependancy for example)
You are right about the Account type , that can be improved.

[NachoPal]

Also #2892 will come to improve and clean up dependancies.