Add classes attributes to set button and pagination color using Swiper css

[benjaminlong]

Adding attributes 'paginationCls' and 'navigationCls' would allow us to use Swiper css classes ('.swiper-pagination-white' and '.swiper-button-white') to set pagination/button colors.

See how swiper use them in its demo: https://github.com/nolimits4web/Swiper/blob/master/demos/16-effect-fade.html#L46

See: benjaminlong@852722c

Following an exemple to create a swiper-container with white pagination/buttons:

{{#swiper-container
    paginationCls='swiper-pagination-white'
    pagination=true
    paginationClickable=true
    navigation=true
    navigationCls='swiper-button-white' }}
...
{{/swiper-container}}

I haven't been able to run ember test though. But it works as expected.

[Matt-Jensen]

Closed by #73