some enhancements

Hi, I set up my server using amavis-mysql. It's not possible to map table names in amavis, and I need them combined with the existing tables from Christoph Haas' tutorial. Also I need this app be run behind a proxy. 

In the next step I'll enhance the app to use amavis (>2.7). I want to make spam settings per domain or user configurable. It will be possible to define groups using the same bayes db. So it could also be interesting for you.

- allow to set main table names
- allow to force host, port, scheme in building links to allow using
  the app behind a transparent proxy
- added configuration hint for using this app behind a proxy to config.ru
- removed datepickr.js call, it's not available