Rebalancing based on arbitrary asset allocation

[marcopus]

This feature is about make portfolio rebalancing based on some arbitrary asset allocations provided by the user. This could be used, for instance, if reference dates are not practical or not desired.

Example

Say we have three funds, A, B and C. The user provides an asset allocation, say like

{
    "A": 20,
    "B": 25,
    "C": 55
}

and the tool makes its rebalancing calculations based on this arbitrary values.