Manually setting shouldEndSession, bug fix and minor code refactoring

This release added a method shouldEndSession() in responseBuilder to enable setting the shouldEndSession value manually.

This release fixed a bug in ListManagementService so that it supports list API call in Japanese skill.

This release used the ServiceError in DirectiveService, it also did minor code refactoring, eg, using const/let instead of var, using single quote instead of double quotes.