feat: add picker selector

[jo-mueller]

Hi @zoccoler, just an extension to the existing selectors: This PR introduces the picker selector, which - as the name suggests - allows to click/select individual points.

I am thinking of adding a callback here that jumps to the last selected object on double-click with the picker-selector enabled, do you think that's a reasonable thing to do? I would then deprecate the highlighting in favor of this approach. I would try to write a pyqtgraph backend next and that would definitely be a bit easier with one less visual layer (color, size, alpha, edge color) to track 🙈

[zoccoler]

Hi @jo-mueller , thanks, I will check this over the weekend. I like the idea! I did not look at the code yet, but just remember to make this backwards compatible for now as other plugins also depend on this. One idea is to let each selector button optionally enabled or not, at least internally. This way, each plugin built on top can choose which features to show or have in the interface. Similar to what I did with the highlighting feature.