Improve typing

[jhsware]

I separated this into two commits (UPDATE: Reverted the second one due to errors that showed up in CD/CI-tests):

• the first I believe is just inconsistencies that I fixed
• the second is my assumption of what the types should be based on:
  • existing export function createRef<T = Element>(): RefObject<T> {
  • how VNode.ref is accessed in mounting.ts

Whereas I am pretty confident about the first commit, the second one needs a closer examination during review.

The part that I want to avoid is the liberal use of any because it makes it harder to contribute code.

[coveralls]

Coverage remained the same at 93.284% when pulling 7b630c210cb8b3b1fd667c7e617bbf7712be6f50 on jhsware:improve-typing into e3c3debff225c3ec0cb25f5ebb650d31298a24a8 on infernojs:master.