Sort button uses only color to indicate whether sort is on

[plweil]

Issue Type (delete the irrelevant ones)

• [x] Bug
• [x] Enhancement Request

Expected Behavior

Sort button should indicate sort direction has been clicked by something other than color-only WCAG Success Criterion 1.4.1

Actual Behavior

Only indication that sort is "on" is that a portion of sort icon turns blue.

I'll submit a PR for this shortly with new sort icons, accompanying logic, css and improved sort button content. The PR will also resolve #851.

[paulrosen]

I overrode the styles and I think that passes:

.vgt-table thead th.sorting-desc button:before {
    border-top: 5px solid transparent;
}
.vgt-table thead th.sorting-asc button:after {
    border-bottom: 5px solid transparent;
}

[plweil]

@paulrosen would you please put that in a CodePen? I've been so swamped that I haven't been able to finish my PR changes. Thanks.