Performance improvements for initial keystrokes in Find

Performance improvements for Find, focused on the initial keystroke or two (when the number of results is usually very high):

- Batch tickmark creation (saves 120ms in med-size files like FindReplace)
- Turn off tickmark & inline highlighting when tons of search results found (saves 1+ sec in huge files like codemirror.js).  We still search the full text, but that's the fast part -- it's just the per-result DOM updates that were slow.

The timing tests I ran involved typing the letter "a" in the Find field in files of varying sizes.  I think in typical files we'll save 50-150 ms, which should be quite noticeable.  In huge files like codemirror.js the improvement will be much more dramatic.