Refactor AP list select portal animation to core utilities, plus new plugin

I'm still not very used to working with git, so I'm afraid this contains rather more changes than I would like.

First set: code/utils_misc.js and plugins/ap-list.user.js - refactor the portal select function from ap-list up to utils_misc. This is a swell animation and very useful; it seems to me that it'd be a good candidate for reuse by other plugins. Rather than have those plugins clone the code, I'd suggest this move.

Second set: a new plugin, list-targets.user.js, which sorts and displays a list of the portals on the map based on how difficult they would be to take down.