Protect generate_graph.pl in table-drawing mode from printing too many rows (by setting a limit in JSON config)

Protect generate_graph.pl in job-drawing mode from printing too many jobs (by setting a limit in JSON config)

cosmetic:  added new commits to README and renamed it Changelog; split out the old README.txt (non-Changelog part)

JobFactory uses $overriding_hash to create jobs/rows from input_id_template; 'input_id' parameter deprecated; standaloneJob supports templates.

Substitution machinery now supports an extra $overriding_hash that contains parameters with higher precedence than the whole of param() structure

fixed several problems with parameter substitution and detection of undefs; added param_required() and param_is_defined()

In case no -logic_name/-analysis_id was supplied, show the list of analyses that have no incoming dataflow (and so are candidates for seeding)