Add support for 'default' and 'options' for taxonomy field

[pshe94]

With this patch user can override in blueprint the taxonomy field to add custom taxonomy values in default and options attributes.
There is only one catch - when overriding default taxonomy field, with both default and options attributes, you need to add validation attribute with type: commalist, as shown in example below. Otherwise, after first save Grav will throw an error at top of the page Array to string conversion, and page won't be saved. But after second try, it will be successful. I haven't found why this happens, but adding validation fixes it. I'm guessing that it might be related to #1024.

taxonomies:
  fields:
    header.taxonomy:
      default:
        category: ['blog','page']
        tag: ['test']
      options:
        category: ['grav']
      validate:
        type: commalist

[rhukster]

Nice improvement 👍

[KennethJoris]

Just what i was looking for GREAT :)
Do add this info to the documentation please

I do see an issue with the other options for this field that don't work anymore (i didn't use the default part as discribed above):

• multiple: false
• validate.required: true

header.taxonomy: type: taxonomy label: 'a label.' multiple: false options: category: ['blog','events','people'] validate: type: commalist required: true