[DataCollector] Improves the readability of the collected arrays in the profiler.

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| License       | MIT

It simply improves the readability of the collected arrays in the profiler:

__before__:
```
Array(date => Array(year => , month => , day => ), time => Array(hour => ))
```

__after__:
```
[
  date => [
      year => , 
      month => , 
      day => 
  ], 
  time => [
      hour => 
  ]
]
```

The errors are also highlighted in the form tree.

![tree](https://f.cloud.github.com/assets/890645/2017660/668966c4-87ff-11e3-9290-7ca11e781520.png)