Text search with a folding editor

Implemented text search for the web folding editor. Similar to the advantage of folding editors in general, that an overview of a whole document can be given while details are blended out (folded), with text search an overview of lots or all text-occurences is visible at once. In Detail finding text works as follows:

1. Highlight all visible occurences.
2. Highlight closed folders with a number of hidden occurences inside.
3. Successively point the cursor to different occurences, possibly open folders for hidden occurences and closing them again if next occurence is elsewhere.