Make it an option to remove the "Save" button, replacing it with "Save and create another"

In some (probably not too common) circumstances, it would be best to replace the "Save" button altogether with "Save and create another". Changing the form from checkbox to radio button with an "Add Save and create another button" and "Replace Save with Save and create another button".

This i would code, against the 7.x branch, if other people want this.

Note: This would also affect the request #291524: Add settings page to check which node types this applies to.