[#527] Avoid extra requests

This calls produce the same request twice on Firefox
Merge pull request #528 from akvo/feature/527

[#527] Avoid extra requests
[#529] RELEASE NOTES v1.6.15
Merge pull request #530 from akvo/feature/529

[#529] Release notes for v1.6.15
Merge branch 'release/1.6.15'
Merge branch 'master' into develop
Merge branch 'develop' of github.com:akvo/akvo-flow into tests/524_clustering