Lots of small code review cleanups from #7809:
* Got rid of unnecessary partial in search-summary-paging.html
* Refactored change notifications in Document to _notifyDocumentChange() method, and fix up similar logic in SpecRunnerUtils.createMockActiveDocument()
* Moved makeDialogFileList from StringUtils to FileUtils
* Renamed "file/item/index" to "fileIndex/itemIndex/matchIndex" for clarity in SearchResultsView
* Return empty array from _getSearchMatches instead of null
* Properly debounce document changes when updating search results view
* Fix up file rename handling in search results view to use indexOf() instead of match()
* Rename "doReplaceAll" event on FindBar to "replaceAll"
* Return a promise from FindInFilesUI.searchAndShowResults()
* Replace calls to _.filter() and _.map() with native JS calls
* Lots of comment/JSDoc improvements