Improve shard bag size selection

[Kenivia]

Currently the shard bag size selection just changes the size (how the price is interpreted), but there's only one actual value being stored (and written to). It'd be good to actually:

1. Show the market price of the other sizes (when the user manually selects the size)
2. Allow manual overwriting of this market price (and store it)

However the actual used shard price should still be the best one. Currently it just uses whatever is inputted (it reads from roster_config.mats_prices). You should:

1. Add another field like shard_prices to roster_config, which should consist of 3 one-cell InputColumns (or one 3-row InputColumn, doesn't really matter) to interface with MaterialCell.
2. Make the shard MaterialCell in BudgetGrid modify shard_prices (As such the shard row in roster_config.mats_prices should just never be read from or written to).
3. Access shard_prices in build_material_info and use the best one.

The relevant files are BudgetGrid, MarketDataFetcher and Payload.ts