ENH Used ordered dictionaries to make the results output predictable.

Replaced ordinary dictionaries with OrderedDicts inside the MTLTester class to make the results output respect the initial order of learners and base learners given by the user.
Remove the unnecessary .iterkeys() calls.
NEW Implemeted a new learning method: OracleLearer.

A special learning method that imitates an 'oracle' who knows which tasks should be merged into the same cluster.
This is done by providing a regular expression that matches the predefined cluster ids from the given tasks' ids.
NEW Implemented a new auxiliary function: log_base_learner_info.

This function logs a report about the given base learners (i.e. their class names and attribute values) to the given logger.