Granular choices for enabling gradient editing in tools

Within the Inkscape preferences it's possible to enable gradient editing for various tools. With this enabled, any gradient stop that is located very close to an editing handle takes priority, making it impossible to drag the handle without first moving the gradient stop out of the way.

For linear gradients this was not much of a concern, as they could be moved perpendicular to the gradient direction to position the stops away from the handles. Radial gradients also rarely present a problem, as it's not very common for their stops to be in the same place as the handles. With the addition of mesh gradients, however, it becomes far more likely that stops will be positioned at the same location as handles, requiring the user to either disable this option in the preferences (for *all* gradient types), or to toggle the mesh visibility via the mesh gradient tool.

For a future version of Inkscape, it would be useful to split the single checkbox into three separate checkboxes, allowing the user to select which of the gradient types should be editable when, for example, the Node and Shape tools are in use.

Exposing a master toggle, which could then be bound to a keyboard shortcut, would also be useful (similar to the grid and snap toggles). The user could then choose which gradient types they wish to edit, but still trivially hide them if they interfere with moving the object's handles.