POM: use HTTPS for schema location URL
POM: use HTTPS for schema location URL

Maven no longer supports plain HTTP for the schema location.

And using HTTP now generates errors in Eclipse (and probably other IDEs).

bigdataviewer/bigdataviewer-core,bogovicj/bigdataviewer-core,bogovicj/bigdataviewer-core,bigdataviewer/bigdataviewer-core