Improve default UI elements position

This is the default UI, maximized:


The most important area, the source code, is very small: even the very small line like `import cadquery as cq` doesn't fit. Also, there are many UI elements, that makes the UI too complex for a new user.

The default UI elements position could be improved.

I suggest something like that:

- main container, vertical split:
- 75% "workspace" container with horizontal split:
- 50% code block;
- 50% rendering block;
- 25% "information" container with horizontal split:
- 67% "text" container, with tabs:
- log viewer
- console
- current traceback
- 33% "inspector container", with tabs:
- Objects
- CQ object inspector
- Variables

Which leads to a lighter and more usable UI: