UI refactoring (WIP)

[dmx974]

• move TopMenubar to LayoutDefault
• simplify SideToolbar and move it to LayoutDefault
• properly integrate canvas creation into vue rendering (instead of creating a DOM-dirty graph-canvas-container)
• refactor to be able to remove all unnecessary tag (it ruins HMR during development)
• start cleaning app.ts to remove $(el) for TopMenubar, SideToolbar and Canvas

[robinjhuang]

@dmx974 Is this still WIP?