In commit 9bba65199e,
the QRCodeWidget was put inside a BoxLayout as a workaround to avoid the "copy to clipboard" and
"save as file" functionality grabbing extra whitespace/stretch/padding and putting it into the
exported image.
However, in turn that commit introduced a bug, where making the dialog larger does not make the
QRCodeWidget larger (which worked prior).
This commit tries to fix the regression and also the original bug.
Sometimes we want its "remember path" behaviour but it does not make sense to
parent the dialog from main window. When so, caller code no longer needs to
get a reference to a main window.
Also rm last usages of get_parent_main_window().
...\electrum\electrum\gui\qt\qrcodewidget.py:88: DeprecationWarning: an integer is required (got type float). Implicit conversion to integers using __int__ is deprecated, and may be removed in a future version of Python.
qp.drawRect(left+c*boxsize, top+r*boxsize, boxsize - 1, boxsize - 1)
The few other cases that used SimpleConfig.get_instance() now
either get passed a config instance, or they try to get a reference
to something else that has a reference to a config.
(see lnsweep, qt/qrcodewidget, qt/qrtextedit)
