A classic Find/Replace dialog including all the options provided
by the QScintilla editor. Additionally a "Replace All" and a
Find All" button are implemented. This complements issue #191
New shortcut in main window for opening the find/replace dialog
connected to the focused widget. Standard for Replace is Ctrl+H.
Consequently the shortcut for Copy with Headers is changed to
Ctrl+Shift+C (see issue #1058).
For SQL text widgets not embedded in the main window, the standard
shortcut cannot be enabled, otherwise it conflicts with the main
window. Therefore the shortcut Ctrl+Shift+H is enabled for all the
SQL widgets as fallback. A better solution would be desirable.
