split kNN by service ID (this should address #13)

classify now looks like:
-group testData by date and get service ID for each date
-group trainingData by date and get serviceID for each date
-store date:service pairs in dict for each testData group
-select trainingData groups that match the relevant service ID
-get indices for the test and training subsets
-run classifier on these subsets
-aggregate statistics for the full test sample.

Also, move getData calls into readData function and pickle for faster
reading. Change training set date range to exclude Jan 6 since no
calendar exists for that date (should fix this problem more generally
by handling the exception)