Rework Step Up: Each kill provides a 2-turn buff that gives 1000% movement...

Rework Step Up: Each kill provides a 2-turn buff that gives 1000% movement speed for several moves, and any action other than moving will remove the buff.
Reasons:
1. removes raw talent level usage & removes old-fashioned callback in Actor.lua
2. makes it more predictable and reliable
3. talent level above 5 gives small bonus