Merge branch 'dev-ced' into opal-1.13.x
Indexing of value sequences fixed.
Fix OPAL-1715: Derived variable cannot be removed
OPAL-1500 Only length and summary are available as aggregation methods.
Merge branch 'opal-1.13.x' of https://github.com/obiba/opal into opal-1.13.x
OPAL-1718 DataSHIELD users can list the methods.
OPAL-1718