Styling update

[atmorling]

Per discussion with @Yun-Wu and @walljcg

• Adds apply_color_map which appends a colormap to the given dataframe. Currently supports user-defined lists of hex values, or an named matplotlib colormap.
• Updates mapping and plotting modules to support a "color column" param, which is used to style.
• also bumps lonboard fork to allow relative placement of custom map widgets.