renamed: DumpController.pm -> DumpOMatic.pm
renamed: DBTool.pm -> SimpleDBTools.pm
db_tool: close #169; refactor main loop into DBTool
Callbacks: close #173; created Callbacks role
Callbacks.pm: issue #173; added 'callback' attribute
Close #173: renamed: Callbacks.pm -> Callback.pm
Callback: issue #173: rename module from Callbacks to Callback
DBTool: close #171: add request_* callbacks
Roles/DatabaseSchema: issue #171; call request_update callback
Roles/Database: don't check for writeable database file in connect()

- fix isa check for "DBI" object in `dbh` attribute