Create first version of VirtualFileSystem

This trait is supposed to replace the RepositoryWorkingDir class. In
addition the RepositoryDatabase will work with the VirtualFileSystem
trait, too, to allow easy accessing of commited content.
Use VirtualFileSystem as working directory

Remove net.secloud.core.RepositoryWorkingDir class and instead use a
more general approach with a virtualized file system defined in the
trait net.secloud.core.VirtualFileSystem as working directory.
Rename RealVirtualFileSystem to NativeFileSystem
First implementation of RepositoryFileSystem

The net.secloud.core.RepositoryFileSystem implements the
net.secloud.core.VirtualFileSystem trait and allows easy accessing of
data in a commit.

Remove VirtualFileSystem methods openRead and openWrite.
Add NullFileSystem

Simple stub for a filesystem, that contains no elements.
Make VirtualFile independent from VirtualFileSystem
Merge (Non)ExecutableFileTreeEntryMode
Merge branch 'dev' into vfs

Conflicts:
	core/src/main/scala/net/secloud/core/Repository.scala
Readd Repository.commit method
Merge branch 'dev' into vfs

Conflicts:
	core/src/main/scala/net/secloud/core/Repository.scala
	core/src/test/scala/net/secloud/core/objects/ObjectSerializerSpec.scala
Merge branch 'dev' into vfs
Create hash algorithm classes in crypto package
Merge branch 'vfs' into bc
Fix AES.name
Integrate crypto package into project

The old net.secloud.core.security package has been remove (except for
one class). Instead the new BouncyCastle supported
net.secloud.core.crypto package has replaced the security package
classes.