Previously it require each plugin to import helpers.py to setup SOCKS proxy.
Now it is enforced by default for all plugins.
Also added a function for plugins to ignore/restore the socket to
default state.
PR #22554.
Notable changes:
1. Prevent excessive engine module imports.
2. Replace trivial usage of `join()`.
3. Keep the output text sorted whenever possible.
4. Close handles properly.
5. Print error to stderr, not stdout.
6. Report search job exit code.
7. Print exception message to stderr if exception was thrown when
running a search job.
8. Utilize XML library to build XML data
And use 2 spaces as indentation.
PR #21098.
Change project directory structure according to application structure.
Change 'nox' configuration option to something more meaningful 'nogui'.
Rename 'Icons' folder to 'icons' (similar to other folders).
Partially add 'nowebui' option support.
Remove QConf project file.
