Date Picker - better highlight disabled days

[boeckMt]

When specifying min and max inputs for available dates on clrDate, those who are out of this range get the class is-disabled.

<clr-date-container>
      <label for="dateControlMax">...</label>
      <input id="dateControlMax" type="date" clrDate formControlName="maxDate"
        [min]="dateRange.min" [max]="dateRange.max" />
</clr-date-container>

Dates which are from the next or previous month get the class is-excluded.

Distinguishing between disabled and excluded dates is very difficult.

Actually a user can override/extend the css class to get the below behaviour, but I think it would be better to use something like crossing out the numbers as a default.

actual view	enhanced view

e.g.

.day-btn.is-disabled {
    position: relative;

    &:before {
      position: absolute;
      content: "";
      left: 0.2em;
      top: 50%;
      right: 0.2em;
      border-top: 1px solid;
      border-color: inherit;

      -webkit-transform: rotate(-45deg);
      -moz-transform: rotate(-45deg);
      -ms-transform: rotate(-45deg);
      -o-transform: rotate(-45deg);
      transform: rotate(-45deg);
    }
  }

[boeckMt]

It would also be good to add the is-disabled class to clr-monthpicker and clr-yearpicker so a user can style this as well, if some years or months are completely excluded.

actual view	enhanced view