view mode for moving and exploding selections arbitrarily

[jimy-byerley]

for exploring and understanding mechanisms, a nice way is often to visually disassemble it or move its parts away. This would be a entirely different tool than the kinematic manipulation since it wouldn't be meant to move parts in a realistic way nor according to predefined paths. And the user should be able to switch from/to the normal (static) mode to the explode (this) mode at any time

• move selections (needs rework selection #6)
• rotate selections (needs (rework selection #6)
• explode selection in a fast way
• reset selection position (relative to upper selection level)