Remove path preview when using action menu or inventory

Fixes
- bug 253.
- using a medikit or psi-amp with a path previewed leaves that
inaccurate path on screen.
- accessing inventory with a path previewed leaves that potentially
inaccurate path on screen.
Update path preview when unit kneels
Merge pull request #634 from cfailde/bug253

Remove path preview when using action menu or inventory