Post Properties Block Delete Option

[herbert8]

Current Behavior

Most 'properties' in the Milling Post can be toggled on and off, meaning that the user can define whether or not they want the corresponding G code to appear in the generated .nc file.

Desired Behavior

Instead of only being able to toggle these properties 'on' and 'off', we'd like to add a third option: 'Optional' (by having three available objects selected from a drop down menu). If 'Optional' is toggled, the code is made an optional block (by using the function writeOptionalBlock instead of writeBlock), which puts the block delete character in front of each line. This allows the user to toggle the code on and off when running on a machine.