refactor(TeacherProjectService): moveObjectUp/Down

[hirokiterashima]

Move these functions from TeacherProjectService to array.ts. It's not really related to TeacherProjectService.

  moveObjectUp(objects: any[], index: number): void {
    if (index !== 0) {
      const object = objects[index];
      objects.splice(index, 1);
      objects.splice(index - 1, 0, object);
    }
  }

  moveObjectDown(objects: any[], index: number): void {
    if (index !== objects.length - 1) {
      const object = objects[index];
      objects.splice(index, 1);
      objects.splice(index + 1, 0, object);
    }
  }