Perishable Spoil Time Filter

Adds a 'spoil time' filter to stockpile and ingredient selectors.

This is a direct port from MrHacky's mod of the same name, found here: https://steamcommunity.com/sharedfiles/filedetails/?id=2178652457
*This mod will be taken down upon request from the original author!*

Source: https://github.com/GhengopelALPHA/rimworld-PerishableSpoilTimeFilter

This allows you to, among other things:

* Automatically turn meat/vegetables about to go bad into chemfuel before it spoils!
* Set up stockpiles in such a way stuff is moved into the freezer only when it needs to be!
* Move decaying animal (or human!) bodies to another location!

Note: The spoil time slider does *NOT* take into account the current temperature of the tile of an item. This may cause the time cutoffs to not be 100% accurate, but it should be close enough anyway. It was done this way to allow setups like the freezer example above, where the item would need to stay in the freezer even though it will never go bad while it is in a freezer tile.