!17 多线程下载合并

* Update README.md
* Improve Features
* 修改获取线路的域名
* 修改默认源
* 修改多线程下载域名和图片服务器
* 修正取消下载的闪退问题
* 将图片下载由 curl 转为 QtNetworkService
* 切换多域名下载，提高下载速度
* 完成并发请求下载

src/spark-store.pro

@@ -25,8 +25,12 @@ DEFINES += QT_DEPRECATED_WARNINGS
 # You can also select to disable deprecated APIs only up to a certain version of Qt.
 #DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000    # disables all the APIs deprecated before Qt 6.0.0
 
+# 禁止输出 qWarning / qDebug 信息
+CONFIG(release, debug|release): DEFINES += QT_NO_WARNING_OUTPUT QT_NO_DEBUG_OUTPUT
+
 SOURCES += main.cpp\
     appitem.cpp \
+    downloadworker.cpp \
     widget.cpp \
     downloadlist.cpp \
     image_show.cpp \
@@ -37,6 +41,7 @@ SOURCES += main.cpp\
 
 HEADERS  += \
     appitem.h \
+    downloadworker.h \
     widget.h \
     downloadlist.h \
     image_show.h \