Handle toolbox category right click (#4969)
Handle toolbox category right click (#4969)

* Handle toolbox category right click

* Stop propagation of right click event

switchinnovations/pxt,playi/pxt,Microsoft/pxt,switch-education/pxt,switch-education/pxt,playi/pxt,switch-education/pxt,Microsoft/pxt,Microsoft/pxt,switch-education/pxt,switchinnovations/pxt,switch-education/pxt,Microsoft/pxt,switchinnovations/pxt,Microsoft/pxt,switchinnovations/pxt,playi/pxt,playi/pxt