[css3-ui] issue triage

Hi Tantek,

Based on our agreement to keep using the wiki for css3-ui issues, and to use a separate page for resolved issues to incrementally build a disposition of comments, I have:

* moved to https://wiki.csswg.org/spec/css4-ui#issues-moved-from-css3-ui all the issues (regardless of status) pertaining to features which have been dropped from the level 3 spec

* moved to https://www.w3.org/wiki/CSS3-UI all the issues which have a resolution which has been acted upon.

https://wiki.csswg.org/spec/css3-ui now only lists issues about which something must be done. Most already have been resolved about, but need an edit to reflect them in the spec. I’ll follow up in separate mails with proposed text.

 - Florian