Merge pull request #693 from makinacorpus/pg_elevation_profile

Switch from python to PostGIS for elevation profiles
Done
Fix tests with new profile formatting
Django security fix release
Merge branch 'pg_elevation_profile'
Positive and negative ascents are now computed using more DEM resolution (fixes #776)
Keep at least 4 points for DEM if geometry length is shorter than sampling resolution
Compute geometry length using higher resolution draped geometry (ref #779, ref #776)
If point is already 3D, keep its Z