* Fix#5313, allow specifying local config path using environment variable and command line flag
* Add command line flag `--localconfig <path>` to specify a file path to use for the local configuration settings.
* Add environment variable support to set config files paths: `KPXC_CONFIG` and `KPXC_CONFIG_LOCAL` to override default locations.
* Reorder startup sequence to load specified config files earlier to allow for theme settings and other early options to be picked up.
* Removed old command line option `--pw`, no longer used.
* Attempt a fix of application not closing when last window is gone. Only set `QApplication::setQuitOnLastWindowClosed(true)` when tray icon is enabled instead of always.
