Reduce app ID hardcoding

And rename the relevant build variable to make more sense

Signed-off-by: Echo J <tcg96nougat@gmail.com>

buildconfig/BuildConfig.h

@@ -52,7 +52,7 @@ class Config {
     QString LAUNCHER_DOMAIN;
     QString LAUNCHER_CONFIGFILE;
     QString LAUNCHER_GIT;
-    QString LAUNCHER_DESKTOPFILENAME;
+    QString LAUNCHER_APPID;
     QString LAUNCHER_SVGFILENAME;
 
     /// The major version number.