activate() {
				return Promise.reject("versions.activate is not implemented");
			}
Interface called to activate a draft.

@param {object} mPropertyBag Property bag
@param {sap.ui.fl.Layer} mPropertyBag.layer Layer
@param {string} mPropertyBag.reference Flex reference
@param {string} mPropertyBag.title Title of the to be activated version
@returns {Promise<sap.ui.fl.Version>} Resolves with list of versions after the activation took place.