correctly handle texts and symbolic coordinates

[thomas-saigre]

This thread is to gather and follow the discussion in #30 about text and sanitation of special characters, especially when symbolic coordinates
/cc @jsaussereau

[thomas-saigre]

def fig19():
    df = pd.DataFrame(dict(
        x = ["A et B", "B", "C", "D"],
        y = [1, 2, 3, 4],
    ))
    fig = px.line(df, x="x", y="y", title="symbolic x coords")
    return fig, "Line Charts with symbolic x coords"

figures with symbolic text containing spaces are resulting in some trouble: as the spaces were converted into _, it resulted in symbolic x coords={A_et_B,B,C,D}, that was causing trouble for LaTeX at compilation, as _ is used for math.

The fix I propose is simply to remove the spaces for this specific case, so "A et B" in Plotly will result in AetB in LaTeX.

Maybe this could be improved ;)