Major revisions and additions to the former HydrophobicWall class, now aka. StickyWall.

Hej Mikael!

Let me know what you think. We should probably move HydrophobicWallLinear inside StickyWall and treat it as just another potential like LJ, r6, r3, etc. I didn't do it because that piece of code isn't mine and I don't like to mess with other people's work without their authorization.

Cheers,

/J
"if" -> "switch" ? Also the depth info is common for all and could be added in the end.