migration from cp_greeting to cp_gender

migration from cp_greeting to cp_gender

this commit replaces commit e09347c89ca119213c4d8ba43083653cda793399 which introduced gender.sql

In database table contacts cp_greeting is removed and instead cp_gender is introduced
For print variables cp_greeting is generated from cp_gender and generic_translations

During migration user gets a chance to
* set gender of contacts where gender couldn't be easily inferred from cp_greeting
* set default greeting (Herr/Frau) for male and female
* transfer any data in cp_greeting that is not gender-related to cp_title

gender.sql is deleted, as there was a risk of losing data in cp_title

Migration code was originally copied from warehouse code