removed Usable by AI allow override, may cause conflicts with updated dashscript

Secondary slot versions are now only available in 'melee' tab

Added to secondary slot under the stealth/melee tags. Slightly reduced dash range - it's now more comparable to the default running speed / isn't just plain better than running.

Changed animation timings and dash script so the knife can dash while sprinting (made possible by having a mutator that allows attacking mid-sprint).
It now looks and works better when used alongside the hit stop and 'run to shot' mutators.

Enabled usable by AI allow override, changed thumbnail.