Don't allow none of layer be created for circle tool.
Don't allow none of layer to be created for spline tool
Don't allow none of layer to be created for draw tool
Don't allow none of layer to be created for polygon tool
Don't allow none of layer to be created for rectangle tool
Don't allow none of layer to be created for star tool
Don't allow none layer to be created for text tool
Don't allow none of layer to be created for gradient tool
Merge pull request #128 from jcome/tool-options-panel-layer-creation

Don't allow none of layer be created (Tool options panel)
Fix loading of WeightedAverage list