Better badge visibility in panel-primary heading

[smmoosavi]

Badges in primary panel heading is gray. please change that like other primary components.

.panel-primary > .panel-heading .badge {
    color: #428bca;
    background-color: #fff;
}

[cvrebert]

Given that the panel colors are customizable, and that adding color-contrast special cases for every possible combination of widgets gets messy, it's questionable whether it's worth adding this.

[cvrebert]

Although, the solution in your new pull request is generic, which largely addresses my concerns.

[smmoosavi]

Move discussion to #13687