Modify TestCase category to use XCTest when included
Modify SenTest specific files use also use XCTest
Duplicate test targets and library targets

We will need separate targets for the library and test targets so we can
modify the targets individually to use XCTest or SenTest.
Modify the defines to be test version agnostic
Change static library name to follow target name
Modify podspec to use subspecs for testing types

The podspec now has a subspec for using SenTestingKit and XCTest. The
default will be SenTestingKit and the only difference between the two
will be the importing of the proper framework.
Fix leftover debug line and new test scheme names
Fixes for comments on PR

* Separate TestCase classes into 2 files
* Create category for NSException to make XCTest similar to SenTest
* Use defines instead of prefix modification to select XCTest or SenTest
* Move Test Step Validation specific defines into that file