supporting custom template engine
refactor server.go accordding to the new template interface
refactor controller.go according to new server interface
refactor results.go according to new server interface
refactor mail components according to new template interface
refactor harness.go according to new template interface
refactor test cases according to new template interface
update booking app.conf
refactor template
refactor RegisterEngine to RegisterTemplateEnginer
supporting custom template engine
refactor server.go accordding to the new template interface
refactor mail components according to new template interface
refactor harness.go according to new template interface
refactor test cases according to new template interface
refactor template
export templateSet and compileError of default TemplateEngine