Change Activity tag to use select2

[pradpnayak]

Overview

https://lab.civicrm.org/dev/core/issues/924

Before

After

[civibot]

(Standard links)

• If this is your first pull-request for CiviCRM, please browse CONTRIBUTING.md for information about the development and testing processes.
• If you are reviewing this pull-request, you may wish to consult the test sites and the Review Standards (long template, short template).

[pradpnayak]

ping @monishdeb

[colemanw]

Most places in the UI now tags are displayed in color. Example from CRM_Activity_Form_Activity:

$tags = CRM_Core_BAO_Tag::getColorTags('civicrm_activity');

if (!empty($tags)) {
  $this->add('select2', 'tag', ts('Tags'), $tags, FALSE, [
    'class' => 'huge',
    'placeholder' => ts('- select -'),
    'multiple' => TRUE,
  ]);
}

But warning this changes the format from an array to a comma-separated list, so the form processing has to deal with that.

[pradpnayak]

@colemanw have pushed the change. Can you please review now?

[monishdeb]

Tested working fine. Merging now.

[colemanw]

Looks good 👍