Make tasks more configurable

[tudor07]

Allow to customise requiresNetworkConnectivity and the others from here:
https://github.com/transistorsoft/transistor-background-fetch/blob/master/ios/TSBackgroundFetch/TSBackgroundFetch/TSBGTask.m#L151

Also expose this to the Flutter plugin: github.com/transistorsoft/flutter_background_fetch

[christocracy]

I’m aware. It’s coming.

[tudor07]

@christocracy I know that it is not nice of me for asking, but... any ETA? I need this feature and if this is not coming any time soon I would need to look into something else

[christocracy]

Within 30 days.

[christocracy]

Be aware, in my experience, these new iOS BackgroundProcessingTasks only seem to fire when the device is plugged into power currently, in spite of:

request.requiresExternalPower = NO;

[tudor07]

@christocracy Thanks a lot for answering and thanks for all the work you put in in this plugin.

[tudor07]

@christocracy Fixed this here: #7
PR to support this in the Flutter plugin here: transistorsoft/flutter_background_fetch#96