Remove tile_storage_idle

Because none of the gegl tests use a mainloop this function
is never tested, and hooking up an idle handler for every
buffer created is somewhat excessive.
operations: Use gegl:load in gegl:layer
operations: improve shift.c

- don't allocate anything, use gegl_buffer_copy instead
- simplify a lot the implementation
- don't enforce the pixel format

though the abyss is enforced to _NONE due to the use of gegl_buffer_copy.
tests: add a test case for gegl:shift
doc: generate the documentation of gegl-random

and properly align files in Makefile.am
Clean up gegl_buffer_get_pixel

* Remove expensive typecheck.
* Inline abyss check.
* Avoid 2nd babl_format_get_bytes_per_pixel call if possible.
* Avoid recalculating tile origin.
Remove more private headers from gegl-operation-*.c
Remove some unused includes
More includes cleanup

gegl-utils.h is part of gegl.h now and doesn't need
an explicit include.
gegl: initialize tile's members before inserting in the cache
gegl: use RAM backend for linear buffers
gegl:crop: Only use public API
gegl:clone: Only use public API
gegl:buffer-source: Remove unused private headers
gegl:path: Use only public API
Fix more introspection annotations for GeglPath

gegl_path_calc_values() is disabled for now.
Remove private headers from gegl-operation-temporal.c
Removed wildcard rules from operations Makefiles

The custom rules prevented automake's dependency tracking from
working, which was generally annoying and made using opencl/*.cl.h
much more painful than necessary.
More includes cleanup
Don't install old generic Makefile to plug-ins dir

Unmaintained and apparently broken for quite a while.