Fix Xcode and Java deprecation warnings

[jnpdx]

This pull request does two things:

1. Fix simple syntax errors and method deprecations (no change in functionality)
2. Replaces the old deprecated NativeAppEventEmitter with RCTEventEmitter

For the first change, everything is pretty straightforward except for two changes I made to error handling -- in both cases. RNFS was tacitly doing some dangerous/unworkable casts (NSException to NSError, NSString to NSInteger). I fixed these, and made the error codes 0 in both cases. If they should have different values, that should be changed before merging.

In order to accommodate the second change, I also had to change the event names, since iOS must supply an exhaustive list of supported events in the supportedEvents method. So, I removed the jobId from the end of the event name since it's used in the body info of the event anyway. In my testing, this doesn't effect multiple simultaneous uploads/downloads in practice.

Deployment target was moved to 8.0 since lots of code was using functionality introduced in 8.0 and thus would've failed anyway on a 7.0 target.

Using Xcode 10.2.1, the project is now free of warnings.

On the Android side, I moved the minimum API version up to 19, since the project was using a method not available until 19 (in conflict with the original min API of 16). This should leave the Android side without warnings and errors as well.

[itinance]

MAny thanks for this! Great work! I will add a specific comment to the event name section.