Issue #208 - On the fly TMX

Almost done, just need to rewrite the tests for the new TMX function and delete the old one.

Added error/success messages and split the code in two views.

@tx2z , does the UI looks good to you?

![1](https://cloud.githubusercontent.com/assets/1294206/3022488/8ba8d4a4-dfc9-11e3-906e-f272033136f5.png)
![2](https://cloud.githubusercontent.com/assets/1294206/3022489/8ba9eb14-dfc9-11e3-8e8b-219d9db70ae2.png)
![3](https://cloud.githubusercontent.com/assets/1294206/3022490/8bab231c-dfc9-11e3-821e-227ed37c0c67.png)

a try/catch wouldn't work here because we are not throwing exceptions and file_put_contents returns False on failure. We can log that instead like:
```php
$empty_TMX = $created_TMX = false;
if ($content) {
    if (! file_put_contents($target_file_path, $content)) {
        // log error to file
    }
} else {
    $empty_TMX = true;
}
```