Second item stash for commonly swapped items

[Kvel2D]

Originally proposed by @Leiyiliro in #253.

Situational items, that you may want to swap depending on the wave on the carry towers. It would be great if there was another stash where you could put those or some other easily accesible way to reach those, or maybe some way to pin them to the start of the bar so find them easily. In the original game I usually kept them on my builder, or had a "storage" tower for those.

[Kvel2D]

This functionality is not needed anymore.

Item stash has been expanded to show 30 items at a time. It is also now possible to open item stash and tower inventory at the same time.