Added fundamental unit tests for NewsSlide.vue and NewsPage.vue

closes #120 (closed)

• Added simple tests (with and without content)
• Subtile refactorings in nearby files
• in NewsPage.spec.ts the last test gets skipped - this is because after wrapper.vm.isLoading = true the problem with the uncatched promise reappears. I wasn't able to pinpoint the problem, but have some ideas how to refactor useNews.ts. As soon as this problem is solved the test should be running fine.