Move download URL construction to ServerInfo.

Centralize creating the URLs so it's not duplicated in two places. This also
allows to change the representation on the server more easily, since it only
requires changes in one place.

Currently only changes URLs for Rockbox builds.

Change-Id: I87277cd61f8b164bdbcd914c9873d674661a786c

rbutil/rbutilqt/base/serverinfo.h

@@ -32,6 +32,8 @@ class ServerInfo : public QObject
         enum ServerInfos {
             CurReleaseVersion,
             CurStatus,
+            CurReleaseUrl,
+            CurDevelUrl,
             BleedingRevision,
             BleedingDate,
         };