Basic html element styling

[anders-kiaer]

Basic html elements should, when used in a webviz instance, have css styling depending on the theme.

As an example, the user should be able to do

import numpy as np
import pandas as pd
from webviz import Webviz, Html

web = Webviz('Example', theme='equinor')

df = pd.DataFrame(np.random.rand(10,3), columns=['A', 'B', 'C'])

web.index.add_content(Html(df.to_html()))

web.write_html("./webviz_table_example")

and get a nicely rendered table using the Equinor theme (in this case). Another use case is tables rendered directly from the current PageElement Markdown.