DDL component fixes

* fix some column definitions (blob, text, integer, bigint, varchar, char)
* add column def (datetime)
* add Index constraint type
* add AlterTableDecorator for Platform
* adjust tests to be compatible with new definitions
well that may be a BC break, but it wasn't working correctly in a first place, as length for blog is completely useless;
I know that BC may be more valuable than correct logic, but I decided against leaving length available