Focus of tags

[felixfbecker]

Other input tag components allow the user to focus tags with the arrow keys and delete the focused one with Delete/Backspace.

Examples:

• https://dev.office.com/fabric#/components/pickers
• https://material.angularjs.org/latest/demo/chips

This is very important for keyboard accessibility, otherwise it is not possible to delete tags in the middle without using a mouse or deleting all the tags in between.

Related to https://github.com/olahol/react-tagsinput/issues/143