Support for SRTM 1 arc second data set (30m)

We have added support for the SRTM 1 arc second dataset, which has been recently released by NASA (link).
The improved resolution makes a noticeable difference, especially in mountainous areas such as the Alps, where the crests are much better defined. See below a comparaison screenshot between the new 30m dataset and the previously used 90m dataset:
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