Support multiple maps on a single Kexi report

- Hide NavigationFloatItem on rendered maps

Due marble bug, maps data have to be in cache.
If there are wrong data on your report (usually
there's only ocean on the map), close it and
reopen, then data should be shown properly.

HttpDownloadManager.h is a part of public Marble
API, but because of another bug there it is not
installed with Marble heders. This file will be
removed when Marble repair thair bug.

BUG:336986
REVIEW:122645