Use <acceptableContext> for mapping TEI license and availability information

[twagoo]

As proposed, but not carried out, in pull request #1, <acceptableContext> can potentially be used to replace the XPath based mapping (see 0fd9632) for the 'availability' and 'license' facets for the CLARIN-DK TEI header profile.

Menzo's (@menzowindhouwer) proposal:

We could try out the <acceptableContext> construct. This allows to say which ConceptLinks on enclosing components are acceptable. And also allow empty context. A problem can be that there are other contextual ConceptLinks that we don't know yet. They have to be explicitly accepted, or we have to go in the code and make the context white/black list potentially more concept specific:
<facetConcept><concept><acceptableContext><concept/></><rejectableContext><concept/></></></>

For more context, see VLO pull request #63.