Automatically display variants added from a VCF file

Currently, Jalview doesn't automatically enable the display of sequence features after an Alignment Window -> File -> VCF Import operation.

This behaviour is inconsistent with other operations which yield features (e.g. import features from file, resolve against database) where their display is automatically enabled. Suggest this inconsistency be removed - so features are shown if the import yielded one or more variant features added to the sequences in the alignment.