feat: enable customizable texts for opened/closed (#1)

[Criban]

https://github.com/Deejayfool/hass-shutter-card/issues/104

@Deejayfool

[jluc2808]

hello @Criban , i just wanted to install your fork, using hacs which point to your repository, i find the deposit , install without problem
But when i want to use it i always get an "this is undefined "
the lovelace item contents;

`type: custom:shutter-card
title: volet sejour
entities:

• entity: cover.volet_sejour
  name: volet sejour
  buttons_position: left
  title_position: bottom
  text_opened: ouvert
  text_closed: ferme`

may i miss something ?

i get control with ressources and th new hass-shutter-card is listed,
to get rid of bord effect, i have desinstalled the provious hass-shutter-card
when i display the code installed it's yours

any help ?