Fixing GEXF parsing in IE.

IE apparently doesn't support getElementsByTagNameNS for XML documents.
if edge weight is set, set size attribute to this value to make setting minEdgeSize and maxEdgeSize effective
add parseJSON plugin
Merge remote-tracking branch 'upstream/master'
Merge remote-tracking branch 'fix-ie-gexf/fix-ie-gexf' into devel
Merge remote-tracking branch 'parse-json/parseJSON' into devel
add interpreter command
make sure attr is in nodesAttributesDict
edge ids can be duplicate in gexf exports of directed graphs, thus do not use the gexf edge id but increment a counter same as in parseGexf plugin
Merge pull request #7 from yaph/devel

ie parseGexf fix, parseJson use unique edgeId, python fix for attributes not in dict. Thanks, yaph.
drop id, label from edges; check for edge attributes not in dict; store weight to size parameter
Fix adding of edges to graph in pushGraph (should be addEdge instead of addNode)
Use required ID attribute when parsing GEXF
Merge remote-tracking branch 'origin/pr/85'

* origin/pr/85:
  Use required ID attribute when parsing GEXF
Merge branch 'pr/73'

* pr/73:
  drop id, label from edges; check for edge attributes not in dict; store weight to size parameter
  add interpreter command make sure attr is in nodesAttributesDict edge ids can be duplicate in gexf exports of directed graphs, thus do not use the gexf edge id but increment a counter same as in parseGexf plugin
  add parseJSON plugin
  if edge weight is set, set size attribute to this value to make setting minEdgeSize and maxEdgeSize effective
  Fixing GEXF parsing in IE.