ttools: add JSON library

This is JSON-java from https://github.com/douglascrockford/JSON-java.git,
commit a9a0762, Mon May 5 15:09:32 2014.

It is currently required for retrieving VizieR table metadata from
the CDS Xmatch service, served in JSON format.
topcat: acquire metadata for VizieR table in CDS xmatch window

Retrieve the metadata from the Xmatch service and display it when
the CDS table is selected.  Improve window cosmetics also.