added files

main class db, interface for layers and pdo-layer class, index
added singleton and config-methods
added new features

add connect and use methods to db-class; added constructor for
query-class (+added this one)
added logic to insert-class
changed insert logic and usage

insert inherited from query and db-class creates insert object instead
of query-object
exception for insert-class, minor changes

minor: class-properties init. with value
created exception class

DatabaseLogicException added as logic-exceptions for database
runtime-errors; changes insert-class exception to DatabaseLogicException
minor changes + little bit phpdoc