Merge pull request #3 from morevnaproject/terms_rework_2

Remove extra word "Spline" for some tool options.
Revert internal name for Set: the menu.
Update type_canvas icon using folder metaphor following the group layer icon design.
Use type_vector_icon instead of type_canvas_icon in library_icon.
Revert action layerencapsulate name which are synfig internals and shouldn't be changed.
Update type_canvas_icon again, this time using cell sheet concept.
Revert some internal names
Rename Group to Set for canvas menu-->Set
Callback the Sets Panel icon.
Use type_canvas_icon instead canvas_icon in Library Panel
to make exported canvases are consistant with valueBase Node in icon style
Replace Control Point with Handle for UI.
The initial desicion is using Control Point to replace Duck for UI
But after finally devs have agreed using the single word is better.