Bring back LUKS code which was previously merged+reverted.

Revert "Revert merge of branch luks-decorator."
This reverts commit efd3179d9508d3d97b5aa1c54e5b817a305538ea.
Messages:
FS::luks is now a decorator for an actual FS composed inside.
Implement cryptOpen/cryptClose/mount/unmount operations.
detectFileSystem, which only uses blkid, is now in FileSystem.cpp.
FileSystem::mount now requires a mountPoint.
Use umount -A to immediately umount all mount points in unmountCmds.
Add override keywords, TODO: add them everywhere.
LibPartedBackend no longer links against libblkid.
Fix LUKS handling in LibPartedBackend::scanDevicePartitions.
Allow detecting FS::Type by path, and remove libparted workaround.
FS detection now only uses blkid (from util-linux).