updated, refactored and cleaned up devkit packaging and releasing scripts.
Relative texture paths in expression fixes

Signed-off-by: Marius Avram <marius.avram1309@gmail.com>
Merge pull request #515 from marius-avram/relative_paths_fixes

Relative texture paths in expression fixes
added two helper hashing methods and refactored code accordingly.

one is a typed variant of foundation::siphash24(), the other one allows to combine two hashes together.
added dummy file to preserve empty directory in git repository.
fixed crash when the geometry inside an assembly that doesn't contain curves changes between two renders.
Merge pull request #513 from est77/OSL

OSL improvements.
Merge branch 'master' of github.com:appleseedhq/appleseed
Fixed PR comment.
Updated DisneyBRDF, refactored and fixed bugs in diffuse component.
Merge branch 'master' of https://github.com/est77/appleseed
Merge pull request #516 from est77/master

DisneyBRDF updates #1
Fixed bug
Importing and exporting disney materials

They are exported using individual files. Currently the settings.xsd
format is used and some extra parameters are added to save the name
and the model of the materials.

Contains also a refactoring of show_message_box() from expressioneditorwindow
which now is required in multiple places. It has been moved to tools.cpp
and renamed to show_warning_message_box().

Signed-off-by: Marius Avram <marius.avram1309@gmail.com>
Merge pull request #517 from marius-avram/import_export_materials

Importing and exporting disney materials
changed default project setup and simplified code.

frame resolution is now 1024x576 (quarter 2K, 1.78 aspect ratio) and film dimensions are 10.24mm x 5.76mm.
Merge branch 'master' of github.com:appleseedhq/appleseed
cosmetics.
fixed comments.
Small disney material editor improvements and fixes.