AcyMailingPlugin: coding style - NO changes on functionality

(to keep it separate from real changes)
AcyMailingPlugin: installer, language file, no root, privacy and more:

- alter installer, added templates and language file
- make all strings localisable
- suppress root category
- disabled contact details until we find a way to respect privacy
- changed layout a bit to have image more in line with title
  and better readable plain text version
- altered copyright / author - PLEASE REVIEW
- version set to 1.9.0
- some little fixes, e.g. html structure