Remember last used solvent and last used container location

[flange-ipb]

Use case (1):
User creates an item and chooses a solvent S. Next time the user creates an item, the solvent S is already selected in the form.

Use case (2):
User creates an item and chooses a location (container C). Next time the user creates an item, the container C is pre-selected.

Thoughts:

• Saving this in the table preferences unsuitable, because it is just a key-value store and solvents/containers are proper database entries, which can be referenced by their id.