Allow experimentation script to take time parameter indicating how long to run (Experimentation.py)

[sidsen]

A user should be able to specify a given time budget for experimentation/tuning and the script should automatically adjust its work to honor that time budget. This requires some careful though/measurement/design. An initial plan could be:

• Measure the time it takes for a single VW pass on the data (this might change depending on the parameters, however).
• Divide up the time budget across the different experimentation areas (learning rate, regularization, feature interaction, estimators). Should the division be equal? Which areas matter more?
• Report the total time taken and best set of parameters found so far.