v0.4.1_WIP_qt-style

Changes from shadps4-emu/shadPS4 (as of now):

• Added "System (Light)" and "System (Dark)" options under View -> Themes. Since I couldn't figure out how to apply different icon colors based on whether or not your system theme is light or dark, they are separate options, so you should use them according to your system colors. Tested on Linux with KDE Plasma. Untested on Windows and macOS, but might be useful on Windows if you use custom system themes.
• Added "Widget Style" options on the Settings menu, with text that shows up on mouse hover. Defaults to "Fusion", as it is currently hardcoded to do so. "System" uses your system's default Qt widget style (example: Breeze, Oxygen, MS Windows 9x, Kvantum). Linux users can override this with the QT_STYLE_OVERRIDE environment variable, as long as it's set to "System". You can tweak this on config.toml with the line widgetStyle = "Fusion". Since I couldn't figure out how to repaint all widgets after clicking on either "Save" or "Apply", this doesn't reflect in real time and you need to close and reopen shadPS4. Tested on Linux with KDE Plasma. Untested on Windows and macOS.

Screenshots (taken on Linux with KDE Plasma):

• "System (Dark)" color theme, "Fusion" widget style

• "System (Light)" color theme, "Fusion" widget style

• "Dark" color theme, "System" widget style (set to Breeze in KDE System Settings)

• "System (Dark)" color theme, "System" widget style (set to Bali10050/Lightly in KDE System Settings)