Mkcd (#1836)
Mkcd (#1836)

* renaming .pxt -> .mkcd

* renaming UI

* updated regex

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