Taxonony: show whole taxonomy path in document editor

When you select a taxonomy term, the document editor show the taxonomy key in the document, but not that path of the taxonomy.

Consider the following taxonomy:

> Places
>> Amsterdam
>> Boston
>> Berlin
> People
>> Amsterdam
>>> Bob
>>> Joe
>> Boston
>>> Sue

The key "Amsterdam" occurs twice, well actually the keys are "amsterdam" and "amsterdam_1", it is the label that occurs twice.

A document marked with amsterdam or amsterdam_1 will simply show "Amsterdam" to the editor. In order to find out if this is Places->Amsterdam or People->Amsterdam the editor needs to edit the document and open the taxonomy browser.

It would be handy and relatively easy to show the taxonomy path in the editor template.

I have attached a patch for the current 2.2.x branch that makes this change.

I think the patch is not complete, we might need to add

1. Configuration to make this change optional

2. A length limit for very deeply nested taxonomy terms, maybe using some notation like Places > ... > Amsterdam for very long paths

3. A fix for org.onehippo.taxonomy.plugin.TaxonomyPickerPluginTest