Basic Alembic support

All in all, this patch adds an Alembic importer, an Alembic exporter,
and a new CacheFile data block which, for now, wraps around an Alembic
archive. This data block is made available through a new modifier ("Mesh
Sequence Cache") as well as a new constraint ("Transform Cache") to
somewhat properly support respectively geometric and transformation data
streaming from alembic caches.

A more in-depth documentation is to be found on the wiki, as well as a
 guide to compile alembic: https://wiki.blender.org/index.php/
User:Kevindietrich/AlembicBasicIo.

Many thanks to everyone involved in this little project, and huge shout
out to "cgstrive" for the thorough testings with Maya, 3ds Max, Houdini
and Realflow as well as @fjuhec, @jensverwiebe and @jasperge for the
custom builds and compile fixes.

Reviewers: sergey, campbellbarton, mont29

Reviewed By: sergey, campbellbarton, mont29

Differential Revision: https://developer.blender.org/D2060

source/blender/python/intern/bpy_app.c

@@ -33,6 +33,7 @@
 
 #include "bpy_app.h"
 
+#include "bpy_app_alembic.h"
 #include "bpy_app_ffmpeg.h"
 #include "bpy_app_ocio.h"
 #include "bpy_app_oiio.h"
@@ -104,6 +105,7 @@ static PyStructSequence_Field app_info_fields[] = {
 	{(char *)"build_system", (char *)"Build system used"},
 
 	/* submodules */
+	{(char *)"alembic", (char *)"Alembic library information backend"},
 	{(char *)"ffmpeg", (char *)"FFmpeg library information backend"},
 	{(char *)"ocio", (char *)"OpenColorIO library information backend"},
 	{(char *)"oiio", (char *)"OpenImageIO library information backend"},
@@ -182,6 +184,7 @@ static PyObject *make_app_info(void)
 	SetBytesItem("Unknown");
 #endif
 
+	SetObjItem(BPY_app_alembic_struct());
 	SetObjItem(BPY_app_ffmpeg_struct());
 	SetObjItem(BPY_app_ocio_struct());
 	SetObjItem(BPY_app_oiio_struct());