Code Quality: Update Stylelint to Match Code Guidelines

[AdamJ]

Update the Stylelint configuration for fabric8-ui to match the HTML/CSS Code Guidelines.

[AdamJ]

Updated the following:

• Required that color variables be either hex codes or PatternFly variables.
  • not allowed: white
  • allowed: #fff or @color-pf-white
• Multiple Declarations require more than one line (cannot have a long string of declarations). not allowed

    .block-1 { font-size: 1.2em; color: @color-pf-white; }

  allowed

    .block-1 {
        font-size: 1.2em;
        color: @color-pf-white;
    }

• Require spaces between blocks for increased readability.

    .block-1 {
        font-size: 1.2em;
    }
  
    .block-2 {
        font-weight: 700;
    }

• Comments must have white spaces between the /* and any text for increased readability.

    /*
    ** This is a proper comment
     */

• Remove allowance of // comments, as they are not supported by CSS
• Add the fr unit to the unit whitelist for future grid use.
• Updated the error message for when a leading zero is added to a property.