Fixed command-line file search interface

argparse complains if a search query is specified using spaces to separate
each search modifier (because argparse assumes that the space means the end of
the argument). Changed to a comma-separated list of search modifiers.
Added optional offset argument to the file_search method

The offset allows for pagenation of search results. This pagenation must be
done manually, but hopefully in the future it can be handled programatically
by this script