Search: do not kill the window when it's closed (remember results when reopening)

[VioletGiraffe]

• Do not kill the window when it's closed (reopen with last search results).
• Switch focus to main window when double-clicking a search result.
• Give the window its own title bar button.
• Title bar: display the total number of scanned entries and the number of search results.
• Search by contents: add a way to select text encoding.