GH-127 GetLocalisedXGMML gathers too many vertices

Filter out global data to activity edges during XGMML parse and not during DOT
file generation.

Fixes GH-127

Signed-off-by: Gordon Smith <gordon.smith@lexisnexis.com>
Merge pull request #128 from GordonSmith/GH-127

GH-127 GetLocalisedXGMML gathers too many vertices

Reviewed-By: Kevin Wang <kevin.wang@lexisnexis.com>
Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>