Relative imports do not work in Spark

[jeroarenas]

Relative imports in topicmodeling.py do not work when running scripts in Spark cluster. Take into account though that:

1/ This can maybe not be as important when not all imports are place at the beginning of the script (there is no need to import everything when running this script).

2/ We are also evaluating whether sparkLDA is going to be kept or removed depending on scalability and performance.