Added non-virtual clone() interface with a virtual private doClone()
method to Workspace and derived classes. Workspaces that had a clone()
method before were adapted to have a common interface everywhere. In
cases where there was no clone() method previously we simply throw an
error for now, until this new functionality is implemented.

Some tests/mocks had to be adapted since there there is a pure virtual
doClone() in all abstract classes.

Do to smart pointer incompatibilities (mainly due to old boost versions)
we had do extract the raw pointer from the unique_ptr returned by clone
and put it into a boost::shared_ptr manually, in some cases. See also
issue 12949.