Added possibility to use browser builtin submit

[stephankaag]

Description

When app need to issue full HTTP POST by browser means (and render resulting HTML), original Formsy was not flexible enough. This PR adds support for using the browser builtin.

V1 patch.

This supersedes christianalfoni/formsy-react#441

[rkuykendall]

Hey @stephankaag and @Nopik

1. Thank you so much for your contribution

2. I think this is a good addition, and I want to add it to Formsy and release it

3. I will try to add it to 1.x but we made releasing WAY easier in 2.x so no guarantees. By the way 2.x is amazing you should upgrade! Very few breaking changes, mostly small renames.

4. Are you cool with this being a 2.0.1 release? I really want to get this out with working types.

5. Again, thank you so much!