* Enable Javascript bindings for photo module.

1. Enable the build flag in build_js.py.
2. Append js into WRAP list of photo’s CMakefiles.txt
3. Add photo module's API into JS API whitelist (embindgen.py)

Exposing the HDR imaging part of photo module.

[TODO]
Add tests
Fix opencv/doc/js_tutorials/

* [WIP] TODO: Add tests

* Remove TonemapDurand: algorithm patented in US, so moved to opencv_contrib

* Fix ningxin's comment: expose the base class.

* Add some more simple binding tests.

Also expose process function