Target allocations on individual holdings

Target allocations are currently set per category and subcategory. To give a single holding its own target today you have to create a subcategory just for it and set the target there, which works but is a workaround.

This request adds the option to set a target weight directly on an individual holding, with no subcategory needed. Per-holding targets would behave like category targets do today: they show up in the allocation view, feed the drift calculation and drive the rebalancing suggestions, for a single portfolio and for a combined portfolio alike.

Vote if you would use this, and comment with how you would want per-holding and per-category targets to sit together.