remove siren and related research
added garrison reaction for siren

- restores the accidentally removed the siren reaction that the garrison
uses in the last commit
Merge pull request #120 from splintermind/gold

Tidyup: removes obsolete siren reactions.
maint-bin: Add our changelog automatically to SWP top-posts
Diseases are now off by default.
Merge branch 'gold' into beta

* gold:
  Diseases are now off by default.
  maint-bin: Add our changelog automatically to SWP top-posts
  added garrison reaction for siren
  remove siren and related research