1. Added an option for a BBH distribution.
2. Setting a local rate to 0.0 or less will disable its generation.
3. Changed default local rates to those quoted in the rates paper.

- expose the GraceDB FAR threshold on the web server
- allow remote modification of the threshold's value

- rename methods associated with web server to make their use more obvious

- fix two typos in last commit

- make timeouts non-fatal, push heart beat buffers downstream instead

- re-organize code in create() method to reduce indentation level

- treat empty input buffers as heart beats, add code to forward 0-length
  buffers out each source pad

- add fap_after_trials() and trials_from_faps() to work with the binomial
  relationship p'=1-(1-p)^m in asymptotic regimes in which direct
  evaluation and inversion of the expression fails

- don't install or include in release tar ball