Bug 859712 - [Gaia][STK] Use new WebAPI to access STK functionality

Please see [bug 859712](https://bugzilla.mozilla.org/show_bug.cgi?id=859712).

I add a checking for IccManager in this patch.
In this way we can make sure it won't break STK function no matter [bug 859220](bug 859712](https://bugzilla.mozilla.org/show_bug.cgi?id=859220) is landed or not. Otherwise, STK function may fail until both bugs are landed. ([bug 859712](https://bugzilla.mozilla.org/show_bug.cgi?id=859712) and [bug 859220](bug 859712](https://bugzilla.mozilla.org/show_bug.cgi?id=859220)).

Thanks