Since the tool knife, when enabled, has no gizmo, users often may not
realize that it is enabled or may not understand how to test it.
This patch proposes to correct this by using the snap gizmo on it.
With this patch the knife tool now uses 2 snap systems.
- The own knife snap system that is used with the shortcut k.
- The snap system of the snap gizmo, which is used whenever the tool is enabled.
This is what it currently does:

