Support boolean values

[dziamid]

Right now if you use boolean values in fixtures.yml, you we not get what you expected:

//task.json
{
  "name": "task",
  "base": "MyPersistedModel",
  "idInjection": true,
  "properties": {
    "completed": {
      "type": "boolean"
    }
}

//fixture/data.yml
task:
  task_1:
    completed: true //will be `true`
  task_2:
    completed: false //will be `true`
  task_3:
    completed: 1 //will be `true`
  task_4:
    completed: 0 //will be `true`
  task_5:
    completed: "1" //will be `true`
  task_6:
    completed: "0" //this is the only what to actually get a `false` value in db