Implement New File page

There is not too much to say. This MR implements the missing /new/{fileType} pages in React.

As intended, the client stores the templates locally and can (automatically and on demand) query templates from the API endpoint.

Issues:

• Since the server is providing the template descriptions as HTML string, the current implementation relies on using React's dangerouslySetInnerHTML feature which is discouraged and a security risk. Particularly, tags will not prevent the default event for their behavior and thus, when clicked, click their DOM parent as well. When clicking the highlighted link in the attached picture, the user will create a file from the template and then be redirected to the link's target page.