Fix srtm2 (ele profile) download. Avoid fko=>mko redirects.

Summary:
Fixed:
- After moving from files.kde.org to maps.kde.org the elevation profile
  data in the srtm2 map theme failed to download.
- After moving to maps.kde.org all queries to tiles on files.kde.org
  caused another http lookup to process the redirect.

Old DGML files keep working, but there is more flexibility now: MarbleServerLayout can be used and still override the server URL and the path. I wonder however if this kind of flexibility is useful?

Reviewers: #marble, rahn

Subscribers: #marble

Projects: #marble

Differential Revision: https://phabricator.kde.org/D830