Autoupdate combinations

[matham]

Same as in signals, if users are allowed to update any properties that determine the combination, after calling init, then you should autoupdate combinations when they are changed, rather than once. Otherwise these properties should be private properties.

For the former, the easiest way to do this is by making them properties that clear the combinations cache that is then re-computed dynamically etc.

Originally posted by @matham in #1 (comment)