qt_themes: add two colorful themes

These two colorful themes are based on the Default and Dark themes, and contain icons that are colored rather than black and white. These icons come from icons8.com and they have been slightly revised by me. I'm pretty sure I was licensed to use them for Citra.

Co-Authored-By: Pengfei Zhu <zhupengfei321@sina.cn>

src/yuzu/uisettings.cpp

@@ -9,6 +9,8 @@ namespace UISettings {
 const Themes themes{{
     {"Default", "default"},
     {"Dark", "qdarkstyle"},
+    {"Colorful", "colorful"},
+    {"Colorful Dark", "colorful_dark"},
 }};
 
 Values values = {};