Use AbstractFeature<dimensions, T>, AbstractGroupedFeature<...>,
AbstractFeatureGroup<...>, FeatureGroup<...> like before and add two
kinds of aliases instead of only one, one with *Basic* for abstract type
and one for Float type.
Partially reverts commit 572efce3f7.
Use AbstractObject<dimensions, T> like before and add two kinds of
aliases instead of only one:
AbstractBasicObject2D<T>/AbstractBasicObject3D<T> for abstract type and
AbstractObject2D/AbstractObject2D for Float.
Makes it easier to use AbstractObject in templates of fixed dimensions
(e.g. Bullet integration, where it can now be written as
`AbstractBasicObject2D<btScalar>` instead of potentially confusing
`AbstractBasicObject<2, btScalar>`).
Partially reverts commit cfd405c32c.
The feature is now templated on shape type, which makes it actually
useful, as it is possible to conveniently query shape parameters from
it. It has now non-templated base and ObjectShapeGroup operates only
with it.