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