Add intersperse component

What does this MR do?

This MR adds a new component: <gl-intersperse>, which separates a list of elements by a given character (the default is , ).

Example:

...
data {
 items = [
    'item 1',
    'item 2',
    'item 3'
  ]
}
...
<gl-intersperse>
  <span v-for="item in items">{{ item }}</span>
</gl-intersperse>

will render:

<span>
  <span>item 1</span>,
  <span>item 2</span>,
  <span>item 3</span>
</span>

Optionally the character used for the last separator can be set independently. Per default it uses the given separator value.

For more information see the added documentation.