For the c++ api dox this expands to "\c nullptr" (the
\c directive indicates a code literal value), and for sipify/Python
it expands to ``None`` (`` is sphinx annotation for literal values)
Makes for nicer dox for both c++ and Python!
within the browser panel
Allows direct export of these files (e.g. to a different format,
crs, etc) without having to actually load them into a project
first.
With implementation in app. This allows GUI library classes to
re-use standard dialogs which are created in app. The initial
use-case is to allow the GUI library symbol list widget to
focus/open an existing Style Manager dialog (created in app),
instead of opening a new modal style manager dialog.
Side benefit - moves some code out of the monolithic qgisapp.cpp
file.
