Blender Git Loki

Allow navigating while transforming

This feature has been desired for some time:
- https://rightclickselect.com/p/ui/Tqbbbc/allow-navigating-while-transforming (See comments);
- D1583;
- T37427;

In short, blocking navigation during transform limits the user to move the object only to visible areas within the screen and hinders the allocation of objects within closed meshes.

The node editor is also impaired because some nodes are far between them and the connectors are too small.

The only disadvantage of this patch (as I see it) is the conflict with the existing key map:
MIDDLEMOUSE:
- enable axis constrain in 3D view;

WHEELDOWNMOUSE, WHEELUPMOUSE, PAGEUPKEY, PAGEDOWNKEY:
- change the threshold of the proportional edit;

So the patch solution was to change these keymaps:
- MIDDLEMOUSE to Alt+MIDDLEMOUSE;
- WHEELDOWNMOUSE, WHEELUPMOUSE, PAGEUPKEY, PAGEDOWNKEY to Alt+(corresponding key);

When you use this new keymap for the first time in the proportional edit, it may seem strange due to the custom of using it (both in View2D and View3D).
But quickly the user gets used to it.

Alternatively we can add an option to the user preferences ([] Allow navigating while transforming). (I'm not much fan of this option).

The patch was done on branch2.8. But maybe it's a good idea to apply it to 2.79

Differential Revision: https://developer.blender.org/D2624