Issue 466 (add/drop PrimaryKeys)

- Updated code styling and added braces.

    - Added drop/add primary key methods to Command.php
    - Added drop/add primary key methods to QueryBuilder.php
    - Added mysql specific dropPrimarykey method
    - Added sqlite specific dropPrimarykey and addPrimaryKey methods
    - Added uint testing for dropPrimarykey and addPrimaryKey methods
    - Corrected postgresql column types, by adding length and precision