Build python module on sandbox.
Macros to build python module on sandbox.
Add options to build appleseed components.
Merge pull request #223 from est77/est

Small CMake related improvements.
small code simplification.
Merge branch 'master' of github.com:jupiter-jazz/appleseed
fixed deployment of _appleseedpython.dll and __init__.py to the sandbox on Windows.
added a clarifying comment.
added a sample renderer to debug tile renderer issues such as half-pixel shifts, etc.
significantly reworked and improved the adaptive image plane sampler.

- improved the noise evaluation algorithm
- replaced the max variation criterion by a quality knob
- got rid of the max contrast criterion
fixed major bug in adaptive image plane sampler.

- the samples need to be scaled to account for the varying density of samples per pixels.
- moved variation tracker into its own file and added a test.
- simplified code.
factorized some code between the uniform and adaptive image samplers.
several refinements to the Render Settings dialog.

- confirm changes when switching to another configuration.
- restore widgets values when canceling the dialog.
fixed crash (introduced in previous commit) when loading a scene after having opened the Render Settings dialog.
the watch_folder.py script can now forward additional, user-supplied arguments to appleseed.
tweaked comment.
the alpha mode of a texture instance may now be set to "detect": the renderer will try to guess which alpha mode to use based on the actual texture contents.
minor tweak in the output of appleseed.cli -h.
fixed parsing of valued command line arguments supporting multiple occurrences (such as the -p parameter in appleseed.cli).
cosmetics.