stat_summary_address() should compute more statistics

I removed the `ip_count` and `ip_propn` computed variables in https://github.com/davidchall/ggip/commit/a55245381d75f9d82a08e9209f524241e25d013e, because it was a very slow computation. I can probably add them back in, if I spend a bit of time with [{profvis}](https://rstudio.github.io/profvis/).