"exclude_from_rendering" flag added into synfig::Layer class
Add "render_excluded_contexts" into RenderDesc
Typo
Modification of Context to provide via this class some information about
current rendering settings into layers which should be rendered.

So we can exclude some layers from final rendering, but keep it on
screen in editor.

Code broken. Compiler errors in dependent classes.
Modify Canvas class to work with new Context.
Some common functions declarations affected, so code becomes more
broken.
Fix synfig::Layer implementation to work with new Context
Fix tergets - Target_Cairo, Target_Cairo_Tile, Target_Scanline,
Target_Tile
Fix Layer_PasteCanvas.

Layer_PasteCanvas::get_bounding_rect() requires ContextParams to
calculate size of content.

So

get_bounding_rect() - now always returns empty rectangle

but
get_full_bounding_rect() - works fine, because this function knows about
Context.

also for Layer_PasteCanvas implemented additional method
get_bounding_rect_context_dependent() which also work fine, because
requires context_params

get_bounding_rect() method uses in duckMatick::add_ducks_layers() only,
so this method should be improved to calculate valid size of
Layer_PasteCanvas
Fix synfig::Layer_Composite
Fix SuperSample (modules/lyr_std)
synfig-core now works
fixed OptionsProcessor
Fixed synfig::synfigapp::CanvasInterface
Fixed synfigapp::Action::LayerDuplicate
Fixed stodio::CanvasView
Fixed studio::WorkArea
Fixed studio::LayerActionManager
Fixed studio::StateEyedrop
All the code is valid and works.
Fixed studio::Dock_Info
Exlude Rectangle from rendering for tests
Enable render_excluded_contexts in workarea and disable in in preview.
Render kept unchanged yet.