Bug/callback not on main thread

[SandeepAggarwal]

This PR fixes the following 2 things:

1. The test cases were not getting compiled due to a linker issue in the Nimble pod
2. The test cases were getting failed randomly due to concurrent behavior in the RemoteFileWatcher protocol
   It not only fixes the test cases but also the expected behaviour from a networking library to get a callback on the main thread.

Code Changes

The callback was executed on the main thread in Remote.swift
The Podfile was updated to have a post-installation script which fixes the linker issue

[krzysztofzablocki]

awesome, thanks for contributing!