Make nodebb-plugin-spoilers compatible with v3

[crazycells]

thanks @baris , I tested and it works but for harmony theme, using data-format leaves an empty space behind, so I changed it to aria-label to remove the whole button...

For those who would like to hide some buttons of the composer can use this CSS code:

.composer .composer-container .formatting-bar .formatting-group {
  [aria-label="Code"], [aria-label="Left align"], [aria-label="Center align"], [aria-label="Right align"], [aria-label="Justify"], [aria-label="Grouped code"] {
    display: none;
  }
}