Search statistics

Added statistics to the search interface:

• The periodic table, checkbox options, and dropdown options now show statistics on the background with bar plot together with an abbreviated count.
• Most filters can be "anchored" to the search results page. In this mode, they show an interactive statistics view. The anchored statistics can be reorganized and they are serialized/deserialized to/from the query string.

Some small changes related to conflicts when merging with datatable:

• In API.js I changed the PropTypes for the APIProvider. When a component accepts children, I always use just PropTypes.node: this supports also list of renderable elements, no need to add arrayOf(PropTypes.node).
• In useScrollResults I don't use debounce for the first hook call, because otherwise, it will wait for half a second on the initial load which is significant for reducing Time to Interactive.