chore(loader): Auto-recognize nested objects supporting namespaces

If the result of any asynchronous loader (regardless function or XHRs) is a nested object, each key will be traversed the object flatten down.

Example:

```json
{
  "DOCUMENT" : {
    "HEADER" : {
      "TITLE" : "Header"
    },
    "SUBHEADER" : {
      "TITLE" : "2. Header"
    },
    "TEXT" : "<em>{{randomValue}}</em> is the answer to life the universe and everything."
  }
}
```

will result into this in `$translationId` internally:

```json
{
  "DOCUMENT.HEADER.TITLE" : "Header",
  "DOCUMENT.SUBHEADER.TITLE" : "2. Header",
  "DOCUMENT.TEXT" : "<em>{{randomValue}}</em> is the answer to life the universe and everything."
}
```

related issue #14
Merge pull request #28 from knalli/namespace-support

chore(loader): Auto-recognize nested objects supporting namespaces