Ston changes

I've tried renaming properties.json/methodProperties.json to properties.ston/methodProperties.ston according to the new Cypress spec. It is related to the [Cypress issue 20] (https://github.com/CampSmalltalk/Cypress/issues/20).

With some simple tests, I confirmed it does not break anything. We can just switch to the new file names without mess. I hope this fix improves the interchangeability with STIG.

Please consider pulling or cherry picking. If you prefer, I can also send you a good-old change set.