Fetaure: Set default taxonomy option

To make it more easier get in comfort of the manual sorting this
feature enables the set of a default param in taxonomy.yml

So you can add for example under chapters configuration:
default: main

With this example every contenttype that uses chapters and has no
manually selected chapter, is preselected with the default chapter
„main“

It fixed the problem, that the Order field is not usable except a
chapter is selected.

Info: This default param feature just works for the behaves_like type
grouping which is relevant for sorting