rewire zip packages inside the virtual filesystem

* change priority of zip packages from "highest" to "just below home dir"
* strict naming rules for zip packages
* require all zips to be below directory "mods/"
* only allow zips to intoduce files below "packages/" (or with a special
  zip package name also below "config/")
* make zip package config persistent (saved to init.cfg)

WARNING: intermediate commit - autodownload system defunct!

DOCREF (removed) addzip removezip

source/src/command.cpp

@@ -1616,7 +1616,7 @@ void deletecfg()
         loopi(sizeof(configs)/sizeof(configs[0]))
         {
             const char *file = findfile(path(configs[i], true), "r");
-            if(!file) continue;
+            if(!file || findfilelocation == FFL_ZIP) continue;
             delfile(file);
         }
     }