Allow override the note model type in the frontmatter for `#card`

[timgreen]

the fields must be [Front, Back].

[timgreen]

one workaroud could be add some special handling for #card-basic-xxx, e.g.

# #card-basic-foo Front content

Back content

==>

{
  model: "basic-foo",
  fields: {
    Front: "Front content",
    Back: "Back content",
  }
}