Add support for custom_card component

[c727]

custom_card is a component to show any custom content on HA frontend like
floorplan or my state-cards 1 2 that currently have to hijack the card of another entity to show up on frontend.
config:

frontend:
  extra_html_url:
    - /local/custom_ui/ha-test-card.html
  extra_html_url_es5:
    - /local/custom_ui/ha-test-card.html
  development_repo: /share/home-assistant-polymer

media_player:
  - platform: cast
    host: 192.168.1.45
custom_card:
  test1:
    full_card: ha-test-card
    more_info_card: ha-test-card
  test2:
    state_card: ha-test-card
    more_info_card: ha-test-card

<dom-module id='ha-test-card'>
  <template>
    <style>

    </style>
    Hello!<br>
    I'm a custom card :-)  ([[stateObj.entity_id]])<button on-tap='onTap'>fire more info</button>
  </template>
</dom-module>

<script>
  Polymer({
    is: 'ha-test-card',
    properties: {
      hass: {
        type: Object,
      },
      stateObj: {
        type: Object,
      },
    },
    
    onTap: function (ev) {     
      this.fire('hass-more-info', { entityId: this.stateObj.entity_id });
      ev.stopPropagation();
    },
  });
</script>

Backend-PR: home-assistant/core#11866

[c727]

What data is OK for stateObj.attributes? I'm sure don't allow me to store my config there...

Should I create an API or are there some other solutions?

Also, how would I share this data for all cards (more-info) instead of calling the API again?

[c727]

Frontend PR should be OK now, changed it to use custom_ui_xxx as Andrey suggested

[andrey-git]

Is there an agreement on the backend PR? If not - let's drop this line change for now

[c727]

You are right, I wanted to avoid merge conflicts in my first approach. Will submit a new PR

[andrey-git]

Use let here and elsewhere in new code.

[c727]

functionality is will be included in frontend entity registry