refactoring database connections

*plugins can provide different database types
*multiple connections will be administrated by the Database Settings
plugin
*first mockup for the db_connections stuff

*mockup for SQL interface and db_sqlite
*db connections only by accident loaded at the right time -> patching
yaspi (locatePlugins) for correct order necessary
working DB connection

*still need to figure out how to load plugins in order
DB Connection list is no settings thing, Connection properties are in
the plugin

*moved the list of connections to lunch_settings (is therefore available
before plugins are loaded)
*connections are edited in the plugin (GUI not there yet)

*Attention: SQLite is not really working with more than one thread
(might be an issue, when statistics are running, and db is queried from
the SQL interface - is fixable)
SQLite multi-threading working

*maybe a bit over-complex, but works
Architecture not perfect... :-( but running ;-)

*closing connections in the end 
*todo: check if connection is still open
Refactoring - no additional functionality
more work on the DB Settings, SQL trace plugin

*renaming SQLite Plugin
*introducing plugin that only traces SQL
*storing database type for every connection possible

TODOs:
*connection specific settings are not stored yet
*storing settings not thread save at all
Working Database Connections

*GUI finished
*seems to be thread safe

TODO: concept to update database handles in plugins
Merge branch 'dbstuff'

Conflicts:
	lunchinator/gui_controller.py