Re-ordering Framework Search Paths
Correct order of RPaths for Debug and Release builds.
[NEW] Migrate old unit tests from OCUnit to XCTest

- Removed the BundleTestRunner which is no longer needed.
- Restructured the test cases
- Load the GPGMail bundle before any tests are executed,
  so we're performing the tests on the debug build and can
  also use GPGMail directly to test messages.
[FIX] Display a proper error message if pinentry is defect. [#627 state:fixed]
[FIX] Display a proper error if decryption fails due to XPC problems.
Merge branch 'dev' of https://github.com/GPGTools/GPGMail into dev