Add url support (downloading) to /plugins install

Additional changes include code refactoring.

tests/unittests/tools/stub_http_download.c

@@ -3,6 +3,7 @@
 
 #include <curl/curl.h>
 #include <pthread.h>
+#include "common.h"
 
 typedef struct prof_win_t ProfWin;
 
@@ -17,6 +18,7 @@ typedef struct http_download_t
     ProfWin* window;
     pthread_t worker;
     int cancel;
+    gboolean silent;
 } HTTPDownload;
 
 void*

tests/unittests/tools/stub_plugin_download.c

@@ -0,0 +1,19 @@
+#ifndef TOOLS_PLUGIN_DOWNLOAD_H
+#define TOOLS_PLUGIN_DOWNLOAD_H
+
+#include <stdlib.h>
+typedef struct prof_win_t ProfWin;
+typedef struct http_download_t HTTPDownload;
+
+void*
+plugin_download_install(void* userdata)
+{
+    return NULL;
+}
+
+void
+plugin_download_add_download(HTTPDownload* download)
+{
+}
+
+#endif