Pacem JS - Tabs

## Tabbed Views

`PacemTabsElement` (alongside with its children `PacemTabElement`s), allow to switch among multiple contents in the same area.

Tabs can be arranged declaratively:

```html
<pacem-tabs orientation="horizontal|vertical" class="tabs-flat|tabs-rise">
    <pacem-tab label="first">
        <!-- tab content -->
    </pacem-tab>
    <pacem-tab label="second">
        <!-- tab content -->
    </pacem-tab>
    <pacem-tab label="third">
        <!-- tab content -->
    </pacem-tab>
    <pacem-tab label="fourth">
        <!-- tab content -->
    </pacem-tab>
</pacem-tabs>
```

## Slotted Labels

`PacemTabElement`s provide a `slot` for customizable complex labels:

```html
<pacem-tab>
    <!-- named slot "label" -->
    <pacem-icon icon="warning" slot="label"></pacem-icon>
    <pacem-text text="{{ 'warning' }}" slot="label"></pacem-text>
</pacem-tab>
```

## Referenced Labels

`PacemTabElement` con refer to a DOM element as a label:

```html
<span id="tabLabel">Label Here</span>

<pacem-tab label="#tabLabel">
    Content Here
</pacem-tab>
```

> The referenced DOM element **gets moved into the label's placeholder** from its original place.