BNCDeviceInfo Crashes On Background Thread

[brianmichel]

When the Branch SDK (by way of the Segment SDK) attempts to create a BNCDeviceInfo instance a WebKit crash is emitted as the BNCDeviceInfo class attempts to execute Javascript on a background thread, which is not allowed with UIWebView. A crash similar to the following is emitted:

* thread #10: tid = 0x7aa758, 0x000000010cf17b2d WebCore`WebCore::FloatingPointEnvironment::saveMainThreadEnvironment() + 45, queue = 'io.segment.analytics', stop reason = EXC_BREAKPOINT (code=EXC_I386_BPT, subcode=0x0)
  * frame #0: 0x000000010cf17b2d WebCore`WebCore::FloatingPointEnvironment::saveMainThreadEnvironment() + 45
    frame #1: 0x000000010db6ad79 WebCore`StartWebThread() + 489
    frame #2: 0x0000000108f30cfc libsystem_pthread.dylib`__pthread_once_handler + 65
    frame #3: 0x0000000108f1db41 libsystem_platform.dylib`_os_once + 36
    frame #4: 0x0000000108f30c9b libsystem_pthread.dylib`pthread_once + 57
    frame #5: 0x000000010ca0c9cb WebKitLegacy`+[WebView(WebPrivate) enableWebThread] + 267
    frame #6: 0x000000010ca09fa4 WebKitLegacy`WebKitInitialize + 52
    frame #7: 0x000000010575d371 UIKit`___UIApplicationLoadWebKit_block_invoke + 217
    frame #8: 0x0000000108b810cd libdispatch.dylib`_dispatch_client_callout + 8
    frame #9: 0x0000000108b661fc libdispatch.dylib`dispatch_once_f + 501
    frame #10: 0x0000000107614efa libobjc.A.dylib`CALLING_SOME_+initialize_METHOD + 19
    frame #11: 0x0000000107615126 libobjc.A.dylib`_class_initialize + 554
    frame #12: 0x000000010761bc1d libobjc.A.dylib`lookUpImpOrForward + 176
    frame #13: 0x000000010762b554 libobjc.A.dylib`_objc_msgSend_uncached + 68
    frame #14: 0x0000000104211560 Branch`-[BNCDeviceInfo init](self=0x00006100000d4890, _cmd="init") + 2608 at BNCDeviceInfo.m:88

The BNCDeviceInfo object should check whether or not it is on the main thread before running the UIWebView code, if it is not, it should dispatch synchronously onto the main thread to configure that property.

[E-B-Smith]

Patch added by @brianmichel in path #517. Thanks Brian!