Multiple upload

Staged: http://wales.pgburton.com/

Switch to using multiple attr on the file upload input. This then adds arrays of info to the $_FILE array. As this is kind of janky; the array is an array of attributes which each then contain the attributes for multiple files.

e.g.

$out = [
  'name' => [
      'a',
      'b'
  ],
  'error' => [
    0,
    0
  ]
];

We don't like this as we can't loop easily over the different files.

Instead we simply pivot the table so it looks more like:

$out = [
  0 => [
    'name' => 'a',
    'error' => 0
  ].
  1 => [
    'name' => 'b',
    'error' => 0
  ].
];

Next we create an $out array which handles the success/error messages, as now we may want to have messages per uploaded file.