Allow users to specify the directory where queries are saved.

[khof312]

Add an optional second argument to run_data_collection(), called output_dir.

• This argument allows users to specify the directory filepath where pySocialWatcher's output should be saved.
• The argument supplied is pre-pended to the filenames of the CSVs that are generated by the program: dataframe_skeleton_*, dataframe_collecting_*, dataframe_collected_finished_*, and collect_finished_clean_*.

This will be helpful to users who generate many files and want to easily see which CSVs correspond to which queries; they can create directories with informative names and store the CSVs inside.

[maraujo]

Pull request reviewed. Thanks for collaborating.