[ENH] Add better error messages + filter out noisy redcap messages

[DESm1th]

This PR:

• Adds a clearer error message when the XNAT server returns an empty file [datman/xnat.py, 01ca591]
• Adds a message that's more useful for debugging when a zip file's intended ID is already in use by another file [bin/dm_link.py, 5a11267]
• Prevents task files from being named with unparseable characters (which can break scripts that use the task files) [bin/dm_task_files.py, 01bd074]
• Allows redcap record IDs matching a regex to be ignored, helping to limit noise when unneeded records may be in the same project [bin/dm_redcap_scan_completed.py, 230d249]