website - new slider

[Dirk Hohndel]

I added something that I wanted to add ages ago and then forgot about (apparently): 
a fifth "slider" with the Subsurface-mobile logo as well as an Android and an iOS icon.

I added this for all languages, but the text should be translated - please send me pull
requests or simply the translation of the one new sentence:

"Using Subsurface-mobile on your Android or iOS device you can access your dive log anywhere"

Thanks

/D