Add JsonWritingTimeoutPoolOutputModule.

This module adds two additional features (needed for the event display)
to the TimeoutPoolOutputModule:

1. file names now follow the DAQ/online convention (files are named
run0001111_lumi0000_streamLabel_hostname.root);

2. for every file written (and after the file is closed), the json file
containing some metadata is produced. This file signals DAQ
services to start merging/distribution of the .root file.