Refactored entity editor classes

Moved classes which were used both in the entityeditor and the
disneymaterialentityeditor:
- LineEditDoubleSliderAdaptor
- ForwardColorChangedSignal

Added new class required by DisneyMaterialEntityEditor:
- LineEditForwarder

Signed-off-by: Marius Avram <marius.avram1309@gmail.com>
DisneyMaterialEntityEditor m_params update on position change

- When the layer position is changed from the interface the
layer_number from the ParamArray containing the model is updated
as well.
- Also when a layer is deleted it is removed from the ParamArray
as well.

The ParamArray is still just a member in the DisneyMaterialEntityEditor
class.

Signed-off-by: Marius Avram <marius.avram1309@gmail.com>