Merge branch 'htmlmail'

* htmlmail: (26 commits)
  changed internal Mailer members from private to protected
  made it possible to disable HTML mails in the config
  removed commented code left from the quoted_printable days
  add missing table tags for HTML diff mails
  fixed subscriber mail signatures
  use real HRs in HTML mails
  Add various headers to the mails FS#2247. pull request #83 closed
  removed footer image from HTML mails
  use inlinestyles for diffs in HTML mails
  fixed signature stripping
  fixed mailprefix handling
  fixed missing replacement for HTML notify mails
  allow image embeds in HTML mail templates
  Added HTML wrapper for mails
  allow non-txt extensions when accessing locales
  added Mailer class to autoloader
  Replaced mail_send calls with new Mailer class
  Make use of new Mailer class in notify()
  Copy all text replacements to HTML replacements in Mailer
  Added setBody() to Mailer class
  ...