Full rework of OC\Files\Storage\Swift in the files_external application

Tested with Rackspace Cloud Files. Following tests are working:

Swift::testTouchCreateFile
Swift::testDirectories
Swift::testRoot
Swift::testFOpen
Swift::testLocal
Swift::testGetPutContents
Swift::testMimeType
Swift::testRecursiveRmdir
Swift::testCopyAndMove

At the moment there are issues with Swift::testStat because it looks like it's not possible to modify the last modification time of objects. I'm working on a solution right now and will push the fix as soon as possible.

In the meantime please test and review the code.