Remove NSData+(Jive)Base64

NSData(NSDataBase64Encoding) already provides base64 encoding
Remove NSData+JiveBase64 from podspec
Prevent deletion of jive-ios-sdk-tests/lib

As the directory is now empty, `git clean` would delete it.
We don't want it to go away as it's used for a group in xcodeproj.
Merge branch 'feature/using-system-base64_encoding' of https://github.com/octiplex/jive-ios-sdk into feature/TABDEV-3100
Merge branch 'feature/TABDEV-3100' into develop
TABDEV-3100: Added the base64Encoding interface to allow building with the iOS 6.0 SDK.
TABDEV-3100: Removed the deprecated flag.
Revert "TABDEV-3100: Removed the deprecated flag."

This reverts commit 48dd3f369bfd5f1a4d8e1b029c19717806dded0d.
Revert "TABDEV-3100: Added the base64Encoding interface to allow building with the iOS 6.0 SDK."

This reverts commit 7ec29ed1edb0951f1e6d236f341e92e24d69deae.
Revert "Merge branch 'feature/TABDEV-3100' into develop"

This reverts commit 86a45da6f249fdb78efad04a9bf8ff28a2638bf6, reversing
changes made to 9fbb7a3b4af65aa13b12b48c849f87e6d8437bb0.