backpack rework

[alexembley]

backpack and other containers should contain items instead of just increasing volume,
so if you drop a backpack all the items in it are still inside the pack.

[Zireael07]

Been suggested multiple times :/

[bug-sniper]

In irc, people have suggested a change where items are assignable to backpacks so that you can drop everything in a backpack in a single action. Perhaps that is what the intention is in this issue report.

[i2amroy]

In irc, people have suggested a change where items are assignable to backpacks so that you can drop everything in a backpack in a single action. Perhaps that is what the intention is in this issue report.

Regardless of intent it's a duplicate of old issues (#3671), so I'm closing this. This is a system we've been wanting to add for a long time, it's just that the inventory system is such a mess nobody has been willing to put in the crazy amount of work it would take to do yet.