Add tool for merging maps

[milo-trujillo]

Say we have two data sets, such as Anonymous and Telecomix. We should be able to merge these in to a single "Hactivism" data set by looking for shared nodes (with the same name) and producing a third combined map joined at these points.

Shared nodes would inherit attributes from the lowest common denominator. For example:

• layer = min(N1.layer, N2.layer)
• retweeted = (N1.retweeted or N2.retweeted)
• mentioned = (N1.mentioned or N2.mentioned)

Let's build a merging tool, with usage like:

$ mergeMaps.py anonymous.gml telecomix.gml combined_hactivism.gml

[milo-trujillo]

Closed with #24