yaml

This changes the format of the required configuration file to yaml, to stay in line with the other conf files. The data inside is the same, but in yaml.
The PR will overwrite any hardcoded default for what is in the config file, and will throw an error should the config file not be found.
If the config file is found, but does not contain the right fields, they will be set to None, and the couchdb module will throw an exception to notify that the connection is not possible. 
I can remove all the defaults, since they have no meaning anymore.