Add support for 7 segment displays

[guillempages]

Add support for 7 segment displays to the hk16t33 component, in addition to the 14 segment alphanumeric displays.

In order to use the 7 segment, an extra type needs to be used on the yaml file.

display:
  - platform: ht16k33_alpha
    id: clock_display
    type: 7Segment
    lambda: |-
      auto time = id(time_sensor).now();
      it.strftime("%H%M", time);
      // use "%H:%M" instead if you want to have the colon lit.