Add tool for making retweet and mention maps

[milo-trujillo]

Once we run SocMap data collection we have all the Tweet data stored locally. Given the list of seed users, we should easily be able to reparse those tweets and build separate maps only based on retweets or mentions. Usage would look something like:

tools/buildMentionMap.py userlist.txt 3 maps/layer2Mentions.gml

tools/buildRTMap.py userlist.txt 3 maps/layer2RTs.gml

This should be very easy if we reuse existing functionality from acquire.py and analyze.py, though we may need to add an extra optional parameter to the mapping functions to override the default filename.

[milo-trujillo]

Implemented. Slight change to the API:

USAGE: ./buildMentionMap.py <userlist.txt> <directory with tweets> <number of layers> <mentions.gml>

USAGE: ./buildRTMap.py <userlist.txt> <directory with tweets> <number of layers> <retweets.gml>