Updated definition of raster planner base class

[marip8]

The current RasterPlanner class hooks for setting the point spacing and minimum hole size, but it turns out that those tasks are not really raster planner specific and can (and should) be done using separate tool path modifiers. This will allow us to reduce the amount of code in the raster planners themselves since these tasks can be defined once as tool path modifiers, and it gives end users more control over the resulting tool paths because they can choose how/if these tasks are performed.

This PR moves the point spacing and min hole size parameters from the raster planner base class into the plane slicer raster planner class. The revision to the plane slicer raster planner in #350 will then remove these parameters (and a few others) from the plane slicer raster planner in favor of using existing mesh modifiers and tool path modifiers to perform those tasks.