Move object classes to net.secloud.core.objects

The most important involved classes are:

* net.secloud.core.ObjectId
* net.secloud.core.Blob
* net.secloud.core.Tree
* net.secloud.core.Commit

Note, that some other classes moved into the new package, too.
Encapsulate serialization objects

The serialization objects are now package private. To access the
(de)seralization methods, one can now use the package object which
exposes them to the public scope. For example:

The object net.secloud.core.objects.Blob is now private and called
net.secloud.core.objects.BlobSerializer. Instead one can call
net.secloud.core.objects.writeBlob(...) and
net.secloud.core.objects.readBlob(...) to access the methods.

The same principle has been applied to trees and commits.
Merge branch 'tmp-restructure' into dev