Running setApplicationIconBadgeNumber on mainThread

[emawby]

This is a UIApplication method so we need to run it on the main thread. It can be run on background threads through wrapper SDKs.

This fixes react-native issue 1262

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This change is 

[jkasten2]

Just a formatting nit, code looks good.

Reviewed 1 of 1 files at r1, all commit messages.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @emawby, @Jeasmine, and @nan-li)

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iOS_SDK/OneSignalSDK/Source/OneSignal.m, line 2225 at r1 (raw file):

    if (fromNotifOpened || wasBadgeSet) {
        [OneSignalHelper runOnMainThread:^{
                    [[UIApplication sharedApplication] setApplicationIconBadgeNumber:0];

nit, remove extra indenting spaces