Typeahead implementation and scope

[mayank99]

Let's use this place to finalize the scope and design of Typeahead / "searchable Select" / Autocomplete (requested in #146). Because there are so many moving parts here, it's worth it to take the time and do this in a proper extensible way from the ground up.

Some features (in order of complexity/importance):

• Type in the input to filter a predefined list.
• Customize icon shown at the end of the input.
• Autocomplete / autosuggest / autoselect the top value in the filtered list.
• Start with empty list and asynchronously load data when a minimum number of letters are typed.
• Start with a small preset list, load more data later (or e.g. perform filtering on server-side).

These are in addition to all the features from our current Select, which includes things like keyboard navigation and accessibility.

Bookmarking some links for reference:

• native <input type=search/> and datalist
• W3 autocomplete combobox
• react-select
• twitter/typeahead.js
• accessible-autocomplete