Make Difference a default value for boolean modifier operation property. Currently operation property of the boolean modifier is set to Intersect, which is the least frequently used boolean operation of the three available. It is also goes out of sync with Intersect (Boolean) tool, where Difference is a default operation. Reviewers: mont29, brecht, sergey Reviewed By: mont29, brecht, sergey Subscribers: mont29, brecht, campbellbarton, sergey, billreynish Tags: #modifiers Differential Revision: https://developer.blender.org/D4340