change signature and usage of get_float4
Safety checks to ensure parsing doesn't run into exceptions.
Added CombineRgb, Mapping, SeperateXyz, CombineXyz to shader
Add new nodes to project file.
Merge branch 'JK1337-combine_separate_nodes'
Reset the progress handler before starting a render session.

Without the reset cancelling and subsequently (re)starting a session
wasn't possible. On the subsequent start the rendering would cancel
immediately since the cancel flag was still raised.