Remove Exceptions from internal API calls except for completionBlock

[RPangrle]

For internal errors they should report back errors using NSError objects either passed in as a method parameter or in a completionBlock callback. The one exception to this is when no completion block is provided.

[RandalliLama]

@RPangrle-MS, did this get addressed?

[kpanwar]

Currently, we throw exceptions only on invalid inputs like nil callbacks, resource and client id.

[RandalliLama]

@kpanwar, per @RPangrle-MS, we should not be throwing exceptions anywhere. I think that it is acceptable to put Asserts in places where argument checking should obviously occurred higher in the stack.

[kpanwar]

The feature work was completed in OSX branch and also merged in to DEV/MASTER.