Canvas properties dialog - Move "Image Span" from "Image Size" to "Image Area"
Canvas properties dialog - Change digits from 10 to 4 for "Bottom Right" and "Top Left"
Canvas properties dialog - Image Area : Change Gtk::Table to Gtk::Box
Canvas properties dialog - Image Area / Keep Ratio - Progress1

- New member var : RendDesc::w_ratio_ and h_ratio_
Used to save the current pixel ratio

- New member function : RendDesc::set_pixel_ratio(int, int)
Used to save the current pixel ratio

- RendDesc::set_x and RendDesc::set_h
Test LINK_IM_ASPECT flag to keep the pixel image ratio based on h_ratio_ and w_ratio_ take care of PX_ASPECT flag
Canvas properties dialog - Image Area / Keep Ratio - Progress2

- Add (temporary) togglebutton to test pixel ratio setting
Canvas properties dialog - Image Area / Keep Ratio - Progress3

- Add chain icon
Canvas properties dialog - Image Area / Keep Ratio - Progress4

- Add a new class : Widget_Link
Widget_Link is a toggle button using "utils_chain_link_icon"

- Use the new class Widget_Link in place of Gtk::ToggleButton in Widget_RendDesc
for the ratio
Canvas properties dialog - Image Area / Keep Ratio - Progress5

The Widget_Link take the charge of active/inactive tooltips
Canvas properties dialog - Image Size / Resolution Ratio

- synfig-core - renddesc
Add LINK_RES flag for resolution ratio
Add x_res_ratio_ and y_res_ratio_ members to record current res ratio
Add set_res_ratio( ) x and y ratio resolution setter
Update set_x_res and set_y_res for LINK_RES flag and cyrrent res ratio

- synfig-studio - renddesc
Add Widget_Link toggle_res_ratio member and toggled signal
Canvas properties dialog - Image Size / Display reduced image ratio

- synfig-core : renddesc
Add get_pixel_ratio_reduced member based on euclide

- synfig-studio : renddesc
Use of get_pixel_ratio_reduced to display the ratio
Widget_RendDesc Image Tab - Remplace deprecated Gtk::Table with Gtk::Grid
Widget_RendDesc - Remplace deprecated Gtk::VBox by Gtk::Box
Widget_RendDesc time tab - Remplace deprecated Gtk::Table with Gtk::Grid
Widget_RendDesc other tab - Remplace deprecated Gtk::Table with Gtk::Grid and Gtk::HBox with Gtk::Box