Make VCS data container classes implicitly shared

Summary:
Also

• rely on default implementation of copy constructor to copy all data on forking the internal data objects
• mark as movable types for improved handling in Qt containers

Object of these classes are created in one place and then passed around
for read-only consumption. They are passed by value in method return
arguments and stored by value. As the classes already have a private
object for pimpl, making this an implicitly shared one is a small step.

Reviewers: KDevelop, apol, mwolff

Reviewed By: KDevelop, apol, mwolff

Subscribers: apol, mwolff, brauch, kdevelop-devel

Differential Revision: https://phabricator.kde.org/D8588