Add basic navigation/interactive components like HiGlass view headers

[sehilyi]

We can add basic navigation/interactive components, such as search boxes for genomic regions, to the Gosling Component. While they are not "visualizations" that fit into the grammar of Gosling, they will be beneficial to have since they are essential for genomics data analysis. Some potential components:

• Search box that searches for genomic regions (and genes if known assembly)
• Export buttons (PNG, JSON, and PDF) like Altair's "..." button.

We can show such components as a header of the Gosling visualization.

I don't think we have to edit the schema (the Gosling grammar). Instead, we can use options for the Gosling Component:

<GoslingComponent ... header={true}/>

cc @ngehlenborg @manzt @etowahadams