Use custom code editor (Emacs, Atom, VS Code…) when opening Pascal source from CGE ed

[DP News-Robot]

A small but important improvement to our CGE editor: Now various commands that open Pascal files can use your custom editor, configured in Preferences -> Code Editor. By default we keep invoking Lazarus but you can now freely change it. This affects a few editor commands: menu item Edit Unit…, menu item Edit Unit Associated …