Introduce AbstractAugmentable
Binding generated code hand-implements handling of augmentations,
which leads to some amount of duplicated code, but notably a lot
of distinct implementations of Augmentatable.augmentation().
We can improve the situation by providing a simple base class which
holds an immutable map of augmentations implementing
AugmentationHolder and Augmentable interfaces.
JIRA: MDSAL-445
Change-Id: I693cd4fbec3d236f039e01448dc4994722b5582d
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>