simplify _customAction logic and add support for a new action - "popup"

[caseyjhol]

Adds support for setting the action to "popup" and streamlines the logic in the _customAction function. Addresses #41. This allows you to use light-popup-card with tap_action out of the box.

Note: I wasn't able to use ESLint as there isn't an ESLint config file.

Example usage:

  - cards:
      - entities:
          - entities:
              - entity: cover.big_garage
                popupExtend:
                  supportedFeaturesTreshold: 8
                tap_action:
                  action: popup
              - entity: switch.porch_light
              - entity: switch.living_room_fan
            popup:
              settings: true
              supportedFeaturesTreshold: -1
              type: 'custom:light-popup-card'

[DBuit]

Hi @caseyjhol

Nice work! Could you also add this option in the readme? than i will merge this :)

[caseyjhol]

@DBuit Done!

[DBuit]

@caseyjhol awesome thanks!