Dump .plugintext, .pluginedit and .plugineditcaption

[cmb]

Hi everybody!

These three classes are relicts of the old plugin loaders, which are rarely used nowadays (partially due to unawareness, partially because they have been superseeded by the newer config forms, and partially because div.plugineditcaption is semantically meaningless). For instance, in the Filebrowser administration there are some remains.

I suggest to get rid of these three classes in core.css, and to remove them also from the common standard plugins which still use them. I don't think this will introduce any real BC break, unless some template applies fancy styles to these classes, but even then it wouln't affect most contemporary plugins.