This is a porting from yii framework version 1.
I need it to run functional tests with fixtures.

issue #2852

Fixes #2571: Fixed the bug that batchInsert will fail for SQLite if the values contain null or boolean false;
Fixes #2683: Fixed the bug that batchInsert will fail for MySQL if the values contain boolean false.

Improved `QueryBuilder::buildLimit()` to support big numbers

tests for this are on elasticsearch branch (due to huge refactoring
there) and will come later by merge

Reverted 0bf2dadd: it's very common to use lower case for column types and upper case for other DB keywords.

- 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