Before this commit, some *.po files contained the same translation
twice within the same file. While this did not led to errors in
gluon yet, it is still invalid. This commit fixes that and removes
the duplicates.

also properly delete location data when a user disables
the location option after re-entering config-mode.

gluon-config-mode-geo-location-osm extends the
gluon-config-mode-geo-location with a location picker based on
OpenStreetMaps.

Based-on-patch-by: Jan-Tarek Butt <tarek@ring0.de>

As already done with other config mode texts, the altitude field now has
default texts that are used when they are not set in the site i18n files.
The altitude-help text has been removed from site i18n; instead, the
geo-location-help text now overrides the whole section description
including the part that mentions the altitude.