Added verifications, if the user has already founded a city and if the city name

Added verifications, if the user has already founded a city and if the city name
is already taken. If the first city shall be founded, a dummy region must be
created, too. Then the city needs to be assigned with it.

The region is more an organizational way of handling more than one city, for
example the user then can apply policies to an entire region and not just a city
or a district.

Signed-off-by: Roland Haeder <roland@mxchange.org>