Blender Git Loki

Nodes: Improvements to edge panning in the node editor.

- New operator property to toggle edge panning in the keymap:
This is disabled by default to avoid edge-panning in cases where it
gets distracting, such as adding a new node. Only the explicit
translate operator(s) (GKEY or drag) have this enabled now.

- Restore the initial view rect on edge pan cancel:
The initial view rect is now stored in the edge pan operator data.
When an operator with edge panning is cancelled it can now call the
`UI_view2d_edge_pan_cancel` function to restore the original View2D
rect.

- Less delay in node editor scrolling:
Delay is useful when scrolling through long lists, such as in the
outliner, but makes node scrolling feel sluggish and unresponsive.
The lower scroll speed here makes a faster response the better option.

- Zoom influence feature:
Somewhat slower scrolling in UI-space when zoomed out. With the 0.5
zoom influence factor nodes behave as if zoom factor is halved,
otherwise it gets too fast when zoomed out. Previously scrolling would
always be constant-speed in UI space, now it's half-way between UI
space and node (view) space.