Improve testability of installation code by refactoring it to completely
separate the GUI and non-GUI code, and to provide more robust support
for non-GUI access to some type of Addon Manager activity.
The code that followed redirects was resulting in a double-download
of the data. This corrects the problem by manually re-queueing a
new network request for each redirect, instead of trying to tell the
QNetworkAccessManager to follow them automatically.
pylupdate does not extract translations when f-strings are used for the
translated text, so all f-strings are migrated to calls to format().
Several other minor translation issues are also addressed.
NOTE: This code has been run through the Black reformatter, which adds
trailing commas in many places that the stock Qt 5.x pylupdate does not
recognize. This code must be processed with the corrected pylupdate to
generate the correct translations.
To enable single-login authenticated proxy use, and simplified multi-threaded
network accesses, this commit adds a new wrapper around a QNetworkAccessManager
and includes a global instantiation of the class intended to exist for the
lifetime of the program. This instance can be used to enqueue any number of
network requests, which the manager will send out to the networking subsystem
in an appropriate manner.
