3.1.0: Typescript support (#188)

* Install typescript.

* Configure TypeScript for declaration output.

* Install @types/classnames

* Install @types/react-dom.

* Declare types.

* Fix optionality.

* Add null guard on clearTimeout.

* declaration:build script

* Fix property type.

* Fix typing.

* Rename declaration:build to build-types.

* Fix type to include children.

* Add typecast.

* Refactor to expose typeguard and fix out-of-bounds issue.

* Repeat type guard to make compile.

* Constraint label to string.

* Fix label proptype.

* Fix Modal's handleOverlayClick

* Added static release artefacts

Co-authored-by: Ernesto Garcia <gnapse@gmail.com>
Co-authored-by: Henning Muszynski <henningmu@users.noreply.github.com>