Renaming mailer text view to match the conventions

As shown above, only after renaming, the plain text view became available:
![contato__asd_and_comparing_indefinido_master___luccamordente_master__luccamordente_hyalin](https://cloud.githubusercontent.com/assets/106093/3702785/0e72e100-1403-11e4-970a-d426bd352802.png)