DB: add additional 'osm:...' tags to result

TODO: query for additional osm:... tags
DB/Osmosis: get usernames by doing a subselect
DB: create extra directories for database types
DB: Create a class for each database type; add to stat-object
DB: on init/update call functions in database type class
Merge pull request #61 from plepe/osmosis-pgsnapshot

Support osmosis pgsnapshot schema as database backend
Merge pull request #63 from plepe/db-database-type-class

DB: create a class for each database
Merge branch 'branch-0.9' into db-additional-tags
DB/Compile SQL: adapt sql queries to database layout
Compile SQL: remove unused code
Compile SQL: tag type 'column': modify value (e.g. for osm_id)
fix
Compile SQL: no need for tag type 'all' => None
Compile SQL: handle None as result of value_format func
DB/Osmosis: convert osm:user to user_id
Merge pull request #62 from plepe/db-additional-tags

Database: additional "osm:..." tags