`pandas.DataFrame.to_html()` without `table border` and `tr style`
The following code produces HTML code for the corresponding table:

```python
import pandas as pd
import numpy as np

df = pd.DataFrame(data=np.arange(3 * 4).reshape(3, 4))
df.to_html(classes=None, border=None, justify=None)
```

Specifically, you get:

```html
<table border="1" class="dataframe">
  <thead>
    <tr style="text-align: right;">
    ...
```

However, both `border` and `style` tags are actually visualization details that should be left for the CSS. The expected behavior should be that the produced HTML should be:

```html
<table>
  <thead>
    <tr>
    ...
```

Besides the problem that there is no way of getting to a clean HTML, this is contradicting the Zen of Python n.2 https://www.python.org/dev/peps/pep-0020/ , where **Explicit is better than implicit.**.

If the default output is something of values for the majority of `pandas` users, the default values for `classes`, `border` and `justify` should be: `classes='dataframe'` (or `classes=('dataframe',)`), `border=1`, `justify='right'`.

(Just tested on the `master` branch).