Refactored app creation, fixed bug when creating an empty set

* splitted yamoda.server module in
** login manager
** jinja filters
** default settings
** app creation (__init__)
* app is created by a function now
* function for loading jinja filters from a given module
* better logging on server start
** show config and config file path (if used)
* moved runserver module

bug fix:
* Exception on empty set creation: check for empty data_id string now

misc:
* Readme update with gunicorn example
* moved buildout config for database modules to separate cfg file