Fix outdated stub factory class for pointcache when Alembic is disabled.

Only use string properties from the cachelib for metadata.

Using ints and floats would require prefixing the Alembic metadata
keys, which becomes messy and ambiguous. Encoding other data types as
strings can be done on the python side as well.

Have to use IDP_ReplaceInGroup to overwrite ID properties that already
exist.

Python UI fix for displaying int and float properties as labels.

Added missing break statements.

Display extra metadata for the cache input archive.

Use ID property groups for storing and loading metadata associated to
Alembic archives.

Two separate property groups for metadata are used (so that reading
caches does not overwrite metadata for output caches).

Write metadata to caches (application name, date of creation, user
description).

Cache library output archives now have a description string next to them
that gets written into the archive.

Display basic metadata of a cache archive in the cache library input
settings.

Silence compiler errors by returning a default value for vector
interpolation.

Support for an optional semantics argument when interpolating cached
properties.

This is necessary to distinguish e.g. vector semantics (linear vs. slerp
interpolation for positional/normal vectors). It would be simpler to
do this based purely on types, but the typing of common Alembic
properties is not sufficiently unique. Semantics arguments are enum
values, that can be omitted if the default interpolation should be used.

Interpolation code for reading Alembic cache samples on subframes.

This features is needed for motion blur. All properties with position
semantics (transform matrices, mesh and curve vertex locations, etc.)
need to be interpolated for fractions of full frames, in order to
reproduce the motion and deformation correctly.

Alternatively we could store subframe time sampling for this subset of
properties. However, this would increase the amount of data stored,
and it might actually show artifacts from subframe interpolation in
Blender which is not visible to animators otherwise and should be
ignored.

Make use of the subframe value in Scene when reading from cache archives.

Subframes are necessary when interpolating values.

Use the Alembic generic chrono_t type internally for reading from
archives, instead of Blender frame values.

This is easier to use for interpolation, the frame value is really only
required externally, before and after reading a sample.

Moved child strand deformation into the general cache processing
function.

Strands processing now has 3 main steps:
1) apply parent modifiers
2) deform child strands
3) apply child modifiers

Allow external object targets for the cache shrinkwrap modifier.

Presets for cached hair simulations.

This requires some modifications to the existing preset python class.
Serializing curve mappings can not be done with a simple property
assignment.

Also the fact that operator confirm popups drop all layout context
pointers means that we have to store the modifier name in the operator
in order to apply the preset to the correct modifier.

Fix for incorrect update callback in haircut cache modifier, leading
to unrelated property changes.

Fix for the hair strands cutting modifier for caches.

The cutoff value was off by 1.0, due to an invalid increment for the
first vertex.

Cleanup and fix for the cache backend factory, due to changed API
functions.