colormanager: Remove hard coded color space

The hard coded color space was causing custom configs to crash if they
didn't contain that specific color space.

Also sets the default role in the config to sRGB EOTF to keep
consistency with previous behaviour

app/node/color/colormanager/colormanager.cpp

@@ -50,7 +50,7 @@ ColorManager::ColorManager() :
 
   // Set config to our built-in default
   SetConfig(GetDefaultConfig());
-  SetDefaultInputColorSpace(QStringLiteral("sRGB OETF"));
+  SetDefaultInputColorSpace(config_->getCanonicalName(OCIO::ROLE_DEFAULT));
 }
 
 OCIO::ConstConfigRcPtr ColorManager::GetConfig() const

app/render/ocioconf/config.ocio

@@ -16,7 +16,7 @@ luma: [0.2126, 0.7152, 0.0722]
 description: A filmlike dynamic range encoding set for Blender
 
 roles:
-  default: Linear
+  default: sRGB OETF
   reference: Linear
   scene_linear: Linear
   data: Non-Colour Data