Created more robust data, upload and download progress tests

Switch test suite to use Given | When | Then structure

Also reworked all tests to be crash safe and fixed the OS X tests.

Bumped version to 1.2.2 and updated CHANGELOG

The task delegate override closure properties now match the formatting used in the session delegate. All closure signatures have been updated to match their method counterparts. Finally, all task delegate method implementations are now being overridden by their respective override closure.

Split Project into Multiple Swift Files

# Conflicts:
#	Source/Alamofire.swift

Data tasks with a registered progress closure will now always call that closure when data is received as well as update the NSProgress object stored in the `TaskDelegate`. The `Request.progress(_:)` method documentation was also updated to reflect the behavior of data tasks.

This addresses the issues reported in #407.

# Conflicts:
#	Source/Alamofire.swift