improve workspace switcher to be more intuitive

Switching workspaces in linux mint is fine, but could be improved to my mind.

the "window view" and the "workspace view" are both sort of "zoom out", but one is done with "up", the other with "down", which is not intuitive.

By calling :
"window view" the one we currently access with "Ctrl+down";
"main view" the default one;
"workspace view" the one we currently access with "Ctrl+up" (to see all workspaces);

I would suggest the following shortcuts :
- Ctrl+Alt+up to zoom in from "workspace view" to "window view", or from "window view" to "main view". the window that was selected in "window view" is shown (like "enter").
- Ctrl+Alt+up on "main view" does nothing
- Ctrl+Alt+down to zoom out from "main view" to "window view", or from "window view" to "workspace view"
- Ctrl+Alt+down on "workspace view" does nothing.

Pressing Ctrl+Alt+up or Ctrl+Alt+down twice is very fast, so no problem I think with it to swich from "main view" to "workspace view". The up/down keys are equivalent to zoom in/out, which is more intuitive.