Added ability to define BG color for extract review

[iLLiCiTiT]

Changes

• it is possible to define background color with presets in ~/pype-config/presets/tools/extract_color.json
  • color must be defined with full hex color format #ffffff (e.g. #fff is not allowed)
• output definition may have defined use_bg_color which says if should use bg color from presets- background color is used only if input's extension can have alpha channel (exr, png, dpx) for others extensions it does not make sence to even try
• it may slow down extract review process as it must create a copy of image, fill it with color and then apply original image on top
• same color is used for global plugin ExtractJPEG and ExtractThumbnail in standalone publisher plugins
  • there is no way how to define if should be used by extract review so use_bg_color attribute was added to have ability turn it off with presets for the plugin

Note

• like I've mentioned in Issue Choose color for alpha in previews #1003 it may break other features and should be properly fixed with Extract review improve rescaling #991
• changes in PR won't change behavior of Nuke's outputs as Review is created in Nuke and ExtractReview won't get alpha input

🏴	this depends on
pype-config	ynput/pype-config#102

[mkolar]

It's working well, however, we should probably make it work also for thumbnails, especially in standalone publisher. It is quite confusing to have a different thumbnail vs the QuickTime itself.