file.filename should be not_analyzed

`file.filename` uses `simple` analyzer which breaks content into tokens on non alphanumeric characters, for example with a dot.

It makes searching on filename not working when doing exact match (filename with extension):

```
GET /mydocs/doc/_search
{
  "query" : {
    "term" : {
        "file.filename" : "annualcompensation_20132014.pdf"
    }
  }
}
```

Closes #53.