set up a separate thread to run note indexing in

• separate thread for the note indexing
• channel to send workspace entry events (and shutdown instructions) to note indexer thread from file scan thread (main thread)
• demonstrate that note indexing thread can access file index
• start implementing path parser
• add comments explaining dbthread operation

relates to #5, #6, and #10 (closed)

todo:

• finish implementing path parser
• convert updater back to a file module