Feature: Cubing logic updates (Conditionally use personal stash, optional requirement for leftover runes when upgrading)

[jasorello]

1. Enable the ability to tell cubing code to leave your personal stash alone
2. Enable the ability to require leftover runes when upgrading runes.

For example, if you said you want at least one leftover rune, you would need to have 4 El runes in your stash before the cubing logic would perform that recipe.

The idea being that you could let the bot do a larger range of automatic upgrades based on drops but still have some leftover for rune words, especially in early ladder.

Is this something people besides me would actually use?