Is active flag

This feature is usefull :)

I did that because I got this error in production:

```
Fatal error: Uncaught exception 'PDOException' with message 'SQLSTATE[23000]: Integrity constraint violation: 1048 Column 'is_active' cannot be null' in /[...]/public/vendor/zendframework/zendframework1/library/Zend/Db/Statement/Pdo.php:228
Stack trace:
#0 /[...]/public/vendor/zendframework/zendframework1/library/Zend/Db/Statement/Pdo.php(228): PDOStatement->execute(Array)
#1 /[...]/public/vendor/zendframework/zendframework1/library/Zend/Db/Statement.php(303): Zend_Db_Statement_Pdo->_execute(Array)
#2 /[...]/public/vendor/zendframework/zendframework1/library/Zend/Db/Adapter/Abstract.php(480): Zend_Db_Statement->execute(Array)
#3 /[...]/public/vendor/zendframework/zendframework1/library/Zend/Db/Adapter/Pdo/Abstract.php(238): Zend_Db_Adapter_Abstract->query('INSERT INTO `us...', Array)
#4 /[...]/public/vendor/zendframework/zendframework1/library/Z in /[...]/public/vendor/zendframework/zendframework1/library/Zend/Db/Statement/Pdo.php on line 235
```
I'm not a fan of boolean parameters:
http://programmers.stackexchange.com/questions/147977/is-it-wrong-to-use-a-boolean-parameter-to-determine-behavior