Don't use `ivy-configure' + display-transformer and undocumented ivy-update-candidates

[kiennq]

Based on #24 but remove the usage of ivy-update-candidates which is undocumented and not working with cons yet.
Also, return filtered result as string since the ivy-action is only accepting string for non alist collection.

[sebastiansturm]

thanks! That seems to fix ivy actions on symbol candidates, and at least with my config there seems to be less flickering during candidate list updates, though I'm not sure if the latter is coincidental. I assume this is also supposed to fix the issues with prescient sorting (which so far I don't use, will have to check how the master branch behaves wrt current ivy versions)?

[kiennq]

assume this is also supposed to fix the issues with prescient sorting (which so far I don't use, will have to check how the master branch behaves wrt current ivy versions)?

I'm not using prescient sorting so I'm not sure about this.
Can anyone that using prescient chime in?

[sebastiansturm]

no point in letting this PR linger forever, as I didn't see anything wrong with it. Will try out your fork once more, then merge it