point_cloud: New dialog to set distribution parameters
point_cloud: New dialog to set distribution parameters

The dialog questioning the user for the distribution's parameters has been completely rewritten.
- The window is now easier to use (one function call)
- The user can choose a color for the points
- Generally a UI that adherese more to ergonomics
- The new structure can be used to query for more than one type of distribution. The window features tabs for each distribution, so new ones can be added easily.

chris-code/DaVis